THE MOST IMPORTANT QUALITY CRITERIA OF SOME HOME- GROWN BLACK-CURRANT VARIETIES. 11. Dry matter, pectin, acid content, colour and formol value. Taina Kuusi The State Institute for Technical Research, Laboratory for Food Research and Technology, Otaniemi Received August 15, 1965 In this work, study of the quality of some home-grown varieties of black- currant was continued; the results concerning the ascorbic acid content have been reported in part I of this series (18). Methods Dry matter was assayed by direct drying with sand in vacuum at 70°C in accordance with the directions given by AOAC (22). Acid content and pH were determined electrometrically, with pH 8.2 as the end-point of titration, applying the method of AOAC (22). The alcohol-insoluble dry matter was assayed by precipitation of the berry homogenate with acid alcohol; the method of Gee et al. was used with slight modi- fications (7). From the air-dry powder obtained in this way, containing not only pectin but also cellulose and other alcohol-insoluble materials, an assay of the pectin proper was made by means of the acid titration method of the above-men- tioned authors (7), and also by the carbazole method according to McCready & McComb (20). The degree of esterification was calculated from the values of the acid titration method. The colour strength was measured at the absorption maximum (520 m/i), and the results were in all cases calculated for the same dilution 2.5 g/100 ml. The formol value was arrived at by application of the method of Wyler (26). Dry matter Table 1 gives the results of analyses for the 3 years, and the general averages, in diminishing order of the latter values. The values for 1962 are from frozen samples, https://www.c-info.fi/en/info/?token=SGCOBq4HXaWzsyl8.rO4xQ010GbxrWCIbd2twNg.vrvDLrNIzE5FXLh4-MhVY09DqBK-m4ZP_EE_z15D1Uv9LB2xfXoK8XH62vlOPfgqd0l8gd-mr0SF7RT6AyN699zPe-PijnHgSLndlgbHwxUF2n0QNXmjvufjty76rvkEFeoW0MXl_zgIRgxEmC8u6iSR0FoZuZ3qBA 283 Table 1. Averages of dry matter assays of black-currant varieties in 1962 1964, and the general averages. 1962 1963 1964 Average Westwick Choice 28.7 28.7 Boskoop 28.2 - 28.2 Wellington XXX 27.9 19.7 20.7 22.7 Silvergieter 27.2 17.5 22.3 Wellington X 23.3 19.0 24.5 22.3 Aström - 22.2 - 22.2 Gerby 21.7 - 20.6 21.2 Roodknop 21.1 - - 21.1 Goliath 24.2 17.4 21.2 20.9 Brödtorp 23.5 19.9 19.2 20.9 Janslunda 24.4 18.9 19.0 20.8 Black of Lepaa 22.3 20.2 18.7 20.4 as the corresponding values for fresh berries seemed to be somewhat unreliable. The other values relate to fresh berries. The results are given as percentages of the fresh weight. Fig. 1 illustrates the sequence of the varieties and the dissimilarities between the different years. The varieties differ to a rather small extent; for instance, the Fig. 1. Dry matter content of black-currant varieties of the 3 years investigated, and general averages. Fig. 2. Dry matter averages and standard devia- tions of black-currant varieties. 284 value of Westwick Choice and Boskoop is probably too high in the same way as the other values of these varieties in that year (1962) are above average. In general the values are lowest in respect of 1963. The order of the varieties deviates consider- ably in the different years. Statistical treatment was effected in the same way as earlier with the ascorbic acid values. In Table 2, there is given for each variety the average, the standard deviation, the number of samples (n) and the limits of variation calculated from the above results (average ± standard deviation), along with the limits of variation observed. Table 2. Statistical testing of the reliability of the dry matter averages. Average St. D. n Limits of variation calculated observed Westwick Choice 28.7 I Boskoop 28.2 I Silvergieter 22.33 ± 5.25 2 17.08-27.58 17.45-27.2 Wellington X 22.3 ± 2.9 3 19.4 -25.2 19.0 -24.5 Aström 22.2 1 Wellington XXX 21.54 ± 3.26 12 18.28-24.80 18.34-29.54 Gerby 21.15 ±0.78 2 20.37-21.93 20.6 -21.7 Roodknop 21.1 1 Goliath 20.92 ± 4.02 3 16.90-24.94 17.35-24.20 Janslunda 20.75 ± 3.16 3 17.59-23.91 18.85-24.40 Brödtorp 20.72 ±2.55 16 18.17-23.27 17.65-25.31 Black of Lepaa 19.85 ±3.44 9 16.41-23.29 16.54-28.03 Fig. 2 indicates the differences between the varieties. Standard deviations are shown as vertical segments. It may be seen that the varieties diverge relatively little in respect to the dry matter. For Westwick Choice and Boskoop, which are highest, the value relates to one single sample; it seems improbable that they would in fact be so much higher than those of the other samples. The significance of the differences between the other varieties was studied statistically by means of the t-test. Here the value of Black of Lepaa, which was lowest, was compared with Silvergieter and Wellington XXX, among the highest. The probability that the dif- ference discovered is not attributable purely to chance is 70 % for Wellington XXX and 60 % for Silvergieter. The significance of the differences is thus not very great. The effect of weather conditions on the dry matter may be studied by comparing the series for the different years. In general, the dry matter was largest in 1962, when the temperature was lowest, and smallest in 1963, when the temperature was highest. It is likely that high temperature favours the general metabolism, which would lead to a loss of dry matter (cf. 4). As regards precipitation, it was thought possible that abundant precipitation in the ripening phase of the berries would increase the water content, and thus diminish the dry matter. However, no such relationship is observable when a comparison is made between the dry matter 285 content ofany variety and the corresponding amount of precipitation in the summer months or in August. It thus seems that abundant precipitation does not induce a direct diminution in the dry matter content of berries. The locality of cultivation does not seem to exert a significant influence upon the dry matter values. The literature contains but scanty detailed information on the dry matter of black-currant. In their table, Turpeinen & Roine (25) give 20 %; according to Beythien & Linzel (cf. 12) the dry matter content is 21 %. Jacobs (13) reports an average of 19.44 %, a minimum of 15.93 % and a maximum of 24.43 % (according to Lampitt & Hughes, 1928, cf. 13, p. 317), and as an average 19.00 %, as a mini- mum 13.7 % and as a maximum 24.4 % (according to Hughes & Maunsell, 1934, cf. 13, p. 318). Souci, Fachmann & Kraut (23) give for black-currant (edible portion) av average of 82.2 g water/ 100 g, i.e. 17.8 % dry matter; the variation limits given are 15.3 21.0 %. For the different varieties, 19.5 % for Boskoop Riesen and 18.5 % for Goliath have been reported by Maurer (19). Groven (11) presents the following values as averages for 4 years: Westwick Choice 20.5 %, Wellington XXX 19.9 %, Boskoop Giant 19.7 %, Brödtorp 18.4 %, Roodknop 18.3 % and Silvergieter 17.7 %. In the present series, the average of all samples was 21.24 %, rather higher than the figures put forward in the literature. The value of dry matter may depend in part upon the method used in the assay. If drying is effected at 100°C, volatile substances other than water may be removed simultane- ously. In the present series, the drying was done at 70°C in vacuum to avoid second- ary changes. For the variety Noir de Bourgogne, grown in France, Gouny & Vangheesdaele (10) report dry matter values, arrived at by the same method as here; they found the maximum value (19.6 %) at picking time; subsequently the value diminishes slightly (19.3 % after a week). In general, published reports do not specify the method of assay, but if the drying has been effected at 100°C, Table 3. Values of alcohol-insoluble dry matter and pectin assayed by the carbazole method for the 3 years, and general averages in diminishing order of the former averages. Alcohol-insoluble dry matter Pectin by carbazole method 1962 1963 1964 Average 1962 1963 1964 Average Wellington XXX 8.9 8.2 9.6 8.9 1.99 1.44 1.69 1.65 Wellington X 7.3 9.2 9.9 8.8 1.50 1.61 1.93 1.68 Astroin 8.7 8.7 1.41 1.41 Gerby 7.3 9.4 8.4 1.08 1.83 1.48 Silvergieter 9.L> 6.2 7.7 2.25 0.96 1.61 Boskoop 7.7 7.7 2.34 2.34 Brödtorp 7.5 7.4 8.0 7.6 1.17 1.21 1.33 1.24 Black of Lepaa 6.9 8.0 7.9 7.6 0.97 1.26 1.39 1.21 Goliath 8.0 6.4 8.1 7.5 1.88 0.94 1.84 1.56 Westwick Choice 7.3 7.3 1.43 1.43 Janslunda 7.3 6.7 7.4 7.1 1.61 1.27 1.50 1.46 Roodknop 5.9 5.9 1.29 1.29 286 Table 4, Values for pectin assayed by the acid titration method, and the degree of esterification for the 3 years, and general averages in the same order as in Table 3. Pectin by acid titration method Degree of esterification % 1962 1963 1964 Average 1962 1963 1964 Average Wellington XXX 2.30 1.83 2.15 2.09 55.7 60.5 54.9 57.0 Wellington X 2.14 2.22 2.21 2.19 62.9 62.9 65.4 63.7 Aström - 2.27 - 2.27 - 64.8 64.8 Gerby 2.52 - 2.10 2.31 47.9 58.9 53.4 Silvergieter 2.45 1.37 1.91 56.3 60.4 58.4 Boskoop 2.53 - 2.53 68.2 68.2 Brödtorp 2.25 1.72 2.01 1.99 53.6 59.0 45.4 52.9 Black of Lepaa 1.50 1.97 1.92 1.80 56.3 64.5 49.1 56.6 Goliath 2.38 1.36 2.09 1.94 65.0 60.8 66.9 64.3 Westwick Choice 2.49 2.49 49.2 49.2 Janslunda 1.92 1.42 1.79 1.71 66.4 64.7 67.2 66.1 Roodknop 1.89 1.89 51.6 51.6 Fig. 3. Pectin, assayed by the acid-titration and carbazole methods, alcohol-insolubledry matter and dry matter of black-currant varieties as averages of 3 years. 287 lower values are found. It might be that a cool climate favours higher dry matter values, as has been hinted at in consideration of the effect of weather conditions on the dry matter. The findings cited in literature relate to countries warmer than Finland. Alcohol-insoluble dry matter, pectin assayed by the carbazole and the acid titration methods, and degree of esterification of pectin The alcohol-insoluble dry matter was isolated from fresh or frozen berries, and stored as air-dry powder until the pectin assays. The results are calculated in g/100 g fresh weight. From the assay of pectin by acid titration, a calculation was made of the degree of esterification to obtain a picture of the type of pectin: the higher the degree of esterification, the more native is the pectin, whereas a low degree of esterification indicates an enzymatic breakdown of pectin. Tables 3 and 4 present the results of these assays. Figures 3—5 illustrate the results arrived at. First, an examination is made of the way in which alcohol-insoluble dry matter and pectin assayed by acid titration Fig. 4. Pectin, assayed by the acid-titration and carbazole methods, and alcohol-insoluble dry matter as averages of values obtained from at least 2 years' results. 288 and carbazole method are changed if the varieties are arranged in diminishing order of the dry matter, and all the values are given the same scale (Fig. 3). It seems that when this scale is employed, the differences in pectin content between the varieties are comparatively small, and the order does not follow that of the dry matter (it is well known that the bulk of dry matter is sugar, which is soluble). In this figure, all the varieties have been taken into account and their averages compared. The picture may be more reliable if the onlyvarieties included are those for which values with respect to more than one year are available. Fig. 4 contains the average values of 8 such varieties, arranged according to the pectin assayed by the carbazole method. Here, it is seen that pectin assayed by the acid titration closely follows the same declining line, with a slight deviation in only the last part of the line. The course of the alcohol-insoluble dry matter is very similar to this line. In Fig. 5 there is a comparison of the values for the different years for the 8 varieties above. This establishes that in 1964, the pectin assayed by the carbazole method was regularly higher than average, whereas in 1963 it was lower than average. Pectin assayed by titration behaved in a similar way and so did alcohol-insoluble dry matter. The findings for 1962 are in line with those for 1964, but the variability is greater. In an examination of the results obtained in these pectin analyses, it is advisable to bear in mind that many different factors may influence the amount of pectin. It is generally known that changes take place in pectin during the ripening of fruits Fig. 5. Alcohol-insoluble dry matter and pectin, assayed by the acid titration and carbazole methods, of black-currant varieties in the different years investigated as compared with the averages. 289 and berries. Particularly in the case of black-currant, it is known that an early crop is suitable for the making of jam and jelly, since at this phase the berries contain an abundance of pectin. By contrast, late crop, in which the pectin is more or less decomposed, is suitable for juice production, where the removal of pectin is essential. In these present studies, the clearly unripe berries were removed before analysis, the degree of maturityhaving been evaluated on the basis of colour. Thus the samples do not contain distinctly unripe berries, although the limit between ripe and over- ripe berries is more difficult to assess. The only indications which could be taken as signs of overripeness are the macroscopically evaluated condition of the berries and, perhaps, a high aroma number. In one case, where the sample contained a particular abundance of unripe berries, separate studies were made of the ripe and unripe parts (sample of Black of Lepaa from Piikkiö, 1963). The following results were obtained: Dry matter Alcohol- Pectin Degree of % insoluble carbaz. acid titr. esterifica- dry matter tion % Unripe sample 17.55 9.0 1.282 2.175 62.05 Ripe sample 18.4 7.5 1.013 1.688 63.9 Accordingly, during maturation there occurs an increase in the dry matter (i.e. the sugar content), whereas the alcohol-insoluble dry matter and pectin diminish (cf. 10). By contrast, in the degree of esterification of the pectin there is no more than a slight change. As the amount of pectin is substantially dependent upon the degree of maturity, and exact definition of this is difficult, it is to be assumed that this fact would impose obstacles to study of the possible differences between the varieties. In Tables 3 —4, there were presented the pectin values for the different varieties, and from these results it is evident that the values obtained by the carba- zole method are systematically lower than those obtained by acid titration. The significance of the differences obtained may be tested statistically. Here it is best to compare the varieties Wellington XXX and Black of Lepaa, where the number of samples was large and where the former evidenced almost the highest value, and the latter almost the lowest. This check gave the following result: n Carbazole method Acid titration method Average St. D. Average St. D. Wellington XXX 11 1.652 ± 0.289 2.061 ± 0.279 Black of Lepaa 9 1.269 ± 0.250 1.839 ± 0.360 Degree of freedom: 18 P 99 % 80 % Thus the difference between these varieties is very significant if the carbazole method is applied. When using the acid titration method the difference lies in the same direction, although its significance is less. In cases where the difference between 290 the varieties is less than here, and there are fewer samples, the significance of the difference is also less, of course. Nevertheless, the above result gives reason to believe that differences do in fact exist between the varieties with respect to the amount of pectin. This fact is interesting from the standpoint of the utilization of black-currant, as a large amount of pectin is advantageous when jam or jelly is being produced, whereas a small amount of pectin is preferable for juice. The largest amount of pectin is found in both Wellington types, whereas Brödtorp, Black of Lepaa, Roodknop and Janslunda contain less pectin. If a comparison is made of the values for the different years, the following results are obtained for the averages of all varieties of the same year: 1962 1963 1 4 General average Alcohol-insoluble dry matter 7.58 7.69 8.54 7.97 Pectin assayed by carbazole method 1.498 1.295 1.534 1.448 Pectin assayed by acid titration method 2.181 1.789 2.032 2.002 Degree of esterification 56.44 65.33 53.96 58.13 The year 1963 was the warmest; then the amount of pectin, as determined by both the carbazole and the acid titration method, was lowest. As for the alcohol- insoluble dry matter, a similar difference is observable between the years 1963 and 1964, but the 1962 value deviates from the series. The value for the degree of es- terification is highest in 1963. In these results, the values arrived at by the carbazole method should be considered most reliable. Consequently the differences between the years, using this assay, were tested statistically by the t-test, and the results were as follows: Year Average St. D. 1962 1.498 ± 0.500 1963 1.295 ± 0.254 1964 1.534 ± 0.259 Degree of Freedom P Difference between 1962-1963 30 80% -»- 1963-1964 33 99% The differences between the general averages of the different years may thus be considered rather well-defined. The averages calculated in this instance also include varieties of which only a single sample from one year and locality was available. If an examination is made of the series in which the same variety was studied in the same locality during the 3 successive years, it is found that the general rule stated above holds good to a great extent. Thus, a high summer temperature seems to diminish the amount of pectin, although its degree of esterification simultaneously remains high. It might be mentioned that, according to Biale (4), apart from sugar, pectin may also serve in the respiration as substrate during fruit storage. 291 On the basis of the above, the assumption might be made that the degree of north latitude of the place of growth could exercise a similar influence on the pectin values, so that in more southern localities the amount of pectin would be less, and the degree of esterification higher than in those further to the north. To check this assumption, there are presented below the values of pectin ob- tained for the different localities: Piikkiö Pälkäne Laukaa Ylistaro Maaninka Rovaniemi Pectin by carbazole method 1.508 1.386 1.541 1.527 1.310 1.094 Pectin by acid titration method 1.910 1.785 2.173 2.305 2.023 1.913 Degree of esteri- fication 63.67 60.14 54.91 48.64 48.76 57.1 Alcohol-insoluble dry matter 7.76 8.0 8.61 8.85 7.54 7.35 The above values indicate the non-validity of the assumption as such. When assayed by the carbazole method, the amount of pectin is of the same order in Piikkiö, Laukaa and Ylistaro, lower in Pälkäne and Maaninka and lowest in Rovaniemi. On assay by the acid titration method, the values are highest in Laukaa, Ylistaro and Maaninka, next come Piikkiö and Rovaniemi, and in Pälkäne the value is lowest. The alcohol-insoluble dry matter is highest in Laukaa and Ylistaro, and diminishes progressively towards the south, but also towards the north (Maaninka and Rova- niemi) the values are lowered. A clear-cut distribution in accord with the degree of north latitude is thus not discernible. In contrast a more distinct tendency is noted in the degree of esterification; the values diminish towards the north, and only the northernmost part deviates somewhat, with the value of Rovaniemi in particular being again higher. If the question is studied, and there are taken into account the values for a single variety in different localities in the same summer (for this, the series in 1964 provide the best fit), it is noted that as regards Wellington XXX a clear-cut in- creasing tendency towards the north occurs in the pectin values assayed by the carbazole method. A similar tendency, with slight deviations, is to be noted in the corresponding values obtained by acid titration. In Black of Lepaa, the results are similar (with Maaninka, the sample of which was overripe, providing an exception). In Brödtorp, too, a corresponding tendency is observable (exceptions being samples of Ylistaro and Maaninka, which suffered from prolonged transport). In the degree of esterification, the same samples show a tendency to diminish towards the north, although the series are somewhat uneven. It might be mentioned that the diminution in the degree of esterification may take place relatively rapidly, so that unevenness in these results is easily brought about. In literature, information on the pectin content of black-currant is rather scanty. Nehring & Krause (21) state only that the pectin content of black-currant is high. Jacobs (13), according to the table of Lampitt & Hughes, (cf. 13. p. 317) give the average of 1.52 % for pectin content, with a maximum value of 1.79 %, and a minimum of 1.37 %. Kertesz (14) refers to the same table, mentioning that 292 the value is the average of 4 assays made by application of the Ca-pectate method. According to Maurer (19), the pectin values of 7 varieties vary between 0.7 2.22 %. Of the varieties, only Boskoop and Goliath were useful for comparison with the present results, and according to Maurer their order differs from that obtained here: for Boskoop, assay by the carbazole method 2.34 %, by acid titration 2.53 %, whereas Maurer finds 1.77 %; for Goliath, assay by the carbazole method 1.56 %, by theacid titration method 1.94%, according to Maurer 2.22%. Tressler & Joslyn (22, p. 728) report values of Bogdanski et al. (5) for Russian berries varying between 0.69—3.15 %. Correspondingly, values for English berries are reported, varying between 0.90 1.25 % (15) or between 0.68 1.45 % (probably according to Charley, cf. 24, p. 728). The Ca-pectate assay method was probably used. It may be that the scantiness of information in literature concerning the pectin content of black-currant can be ascribed to the fact that the industry utilizing black-currant is little interested in the amount of pectin in black-currant, as the main product is juice, and in juice production, pectin has to be removed in any case. In the British method, asreferred to by Tressler&Joslyn (24), pectin is completely removed to obtain juice of which the stability is fully guaranteed. In contrast, the German method allows of the retention of some pectin in the juice; for instance, in the tables of Koch & Zeyen (17), the pectin content in pure juice is 0.41 g, in pomace extract 0.07 g and in the blend 0.35 g/100 ml. This pectin remaining in the juice is rather highly esterified, and makes the juice rather viscous; Koch considers this to be important from the point of view of aroma, when juice of the »Siissmost» type is being produced. Again, those engaged in horticultural studies evidently do not consider the pectin content important from the point of view of plant-breeding, and thus little attention has been paid to the pectin content by these investigators. Table 5. Acid content of black-currant varieties according to analyses during 3 years, and the general averages. Fresh weight Dry matter 1962 1963 1964 Average 1962 1963 1964 Average Boskoop 708 Ti is 2511 2511 Roodknop 674 674 3200 3200 Äström 628 - 628 2829 2829 Janslunda 632 626 555 604 2586 3320 2921 2942 Westwick Choice 574 - - 574 1997 1997 Gerby 640 500 570 2946 2427 2687 Black of I.epaa 634 564 510 569 3051 2824 2728 2868 Brodtorp 620 561 504 562 2589 2886 2625 2700 Wellington XXX 611 547 481 546 2184 2794 2328 2435 Goliath 562 498 477 512 2327 2870 2250 2482 Silvergieter 530 487 509 1696 2791 2244 Wellington X 546 471 412 474 2348 2479 2117 2315 293 Table 6. Statistical testing of the reliability of averages of acid content. Limits of variation Average St. I). n calculated observed Roskoop 708 1 Roodknop 674 1 Äström 028 1 Janslunda 604 ±43 3 571-647 555-632 Westwick Choice 574 1 Gerby 570 ±99 2 471-669 500-640 Brödtorp 560 64 16 496-624 462-670 Black of Lepaa 550 ±56 9 494-606 475-636 Wellington XXX 525 ±62 12 463-587 431-662 Goliath 512 ±44 3 468-556 477-562 Silvergieter 509 ±3O 2 479-539 487-530 Wellington X 476 ±67 3 409-543 412-546 Fig. 6. Acid content of black-currant varieties, on fresh weight and on dry matter, in the 3 years investigated, and general averages. 294 Acid content and pH Table 5 presents the acid titration values for the varieties in the 3 years, and the general averages are presented in diminishing order. For 1962, the values relate to frozen berries, and the others to fresh ones: in the former case the values from the fresh berries were not wholly reliable. The values are given in ml 0.1 n NaOH/100 g of berries, and acid content is calculated both on fresh weight and on dry matter. Fig. 6 illustrates the sequence of the varieties, and the divergences between the different years. The values of the varieties ot which only one sample was studied are shown in the left hand corner of the diagram. It may be seen that the acid content, fresh weight, was in 1962 higher than average, and in 1964 lower than aver- age. Calculated on dry matter, the values were highest in 1963, when the dry matter values were lowest, and lowest in 1964. In 1962, both the acid content and the dry matter were high, and thus the acid content, dry matter, remains generally low. The order of the varieties varies but little between the different years. Statistical checking of the reliability of the averages was carried out in the same way as before. In Table 6, there are given the average, standard deviation and number of samples (n) for each variety, along with the calculated and observed limits of variation. Fig. 7 visualizes the differences between the varieties. The standard deviations are indicated as vertical segments. Particularly as regards Gerby, the deviation is large. The ranges of acid content for the different varieties in many cases markedly overlap, so that their order may easily be reversed in other series of analyses. The figure also contains the corresponding values of total ascorbic acid, with a view to checking whether any correlation exists between acid content and amount Fig. 7. Acid content averages and standard devia- tions of black-currant varieties, and correspond- ing total ascorbic acid values. 295 Table 7. The pH values of black-currant varieties for the 3 years, and the general averages. 1962 1963 1964 Average Wellington XXX 3.57 3.36 3.03 3.22 Janslunda 3.40 3.38 2.95 3.24 Black of Lepaa 3.46 3.34 3.12 3.24 Gerby 3.49 3.05 3.27 Brödtorp 3.47 3.39 3.10 3.30 Aström - 3.30 3.30 Goliath 3.43 3.40 3.10 3.31 Wellington X 3.41 3.55 3.25 3.40 Roodknop 3.45 3.45 Silvergieter 3.41 3.50 3.46 Boskoop 3.50 3.50 Westwick Choice 3.60 3.60 of ascorbic acid, as has been assumed (cf. 6). No perfect correlation is noted, but some parallelism seems to occur. In respect of pH, the values among the different varieties vary but little. In Table 7, the variety average of the different years and the general averages are given in the order of the latter. Fig. 8 provides a comparison of the different years. On the left it is observable that in 1964 the values were systematically lower than average, whereas in 1962 and 1963the values were in general higher than average. Nevertheless, the differences 5 Fig. 8. Values of pH of black-currant varieties. On the left: values for the different years and general averages. On the right: correlation of acid content and pH in the different years. 296 are only small. In the diagram, in the right hand comer, there is indicated the correlation between the acid content and pH. Each year, a higher acid content corresponds to a lower pH, but the change in pH is much smaller than that in acid content. In all, the different years are slightly dissimilar, so that the diminution in pH due to acid content was least in 1962, and most marked in 1964. It has been suggested (9) that in the Far North the currants would contain more acid and less sugar than those further south. If a study is made of how far the temperature of summer influences the acid content, some correlation is found when acid content and the cumulative total of heat of a sample are compared, although the variety, the degree of maturity and other factors may induce variability. Pre- cipitation does not seem to exercise a systematic influence. By contrast, the amount of sunshine appears to be important. In 1962, when the acid content was highest, the least sunshine was recorded, whereas both 1963 and 1964 were sunny years. When the acid content and the totals of hours of sunshine were compared, with respect to all the samples, a comparatively clear-cut negative correlation was observed, i.e. the less the total of sunshine, the higher is the acid content. Comparison of the acid content values obtained here with those reported in literature shows that the former are regularly higher than, for instance, those given Fig. 9. Correlation between acid content and corresponding sunshine values. 297 by Jacobs (13): maximum 622, average 499, and minimum 121 ml 0.1 n NaOH/100 g; the variety is not quoted. Baumann (2) reports an acid content of 3 %, which if calculated as citric acid corresponds to 469 ml 0.1 n acid/100 g. As a general rule, it seems that Finnish-grown black-currant contains more acid than that of Central Europe. Souci (23) gives for black-currant 3.03 g citric acid/100 g and 0.4 g malic acid/100 g, which would together mean 533 ml 0.1 n NaOH/100 g. This is higher than the above-mentioned values given in literature. For the different varieties, Baumann (3) gives values representing g total acid per litre of juice. Comparison of the varieties studied with the present results shows that the sequence is nearly the same in both cases; Baumann emphasizes that lack of sunshine increases the acid content. Further, Koch & Bretthauer (16) and Groven (11) report acid content values for juices pressed from different varieties. Grovens values are comparatively low, and the differences between the varieties small. The results of Koch correspond approximately to the results of Baumann, and also to the present values. Table 8, Values for colour strength of black-currant varieties during the 3 years, and the general averages, in diminishing order of the latter. 1962 1963 1964 Average Boskoop 988 - 988 Äström 890 890 Silvergieter 522 872 697 Wellington X 490 889 668 682 Janslunda 633 930 401 655 Roodknop 591 591 Brödtorp 598 651 496 582 Goliath 571 700 392 554 Black of Lepaa 528 655 370 518 Wellington XXX 471 647 389 503 Westwick Choice 486 486 Gerby 519 - 371 445 Colour strength In Table 8, there are compiled the values for the 3 years and the general aver- ages, in the order of the latter. In 1962, the values were obtained from frozen samples and the others from fresh ones. The absorption readings have been calculated for the dilution of 2.5 g/100 ml, and measurement was made at 520 my, in general the maximum point. Fig. 10 illustrates the results. It is observable that the values were highest in 1963 and lowest in 1964. The order of the varieties in the different years shows considerable variation. 298 Statistical testing of the reliability of the differences found between the varieties is in this case less useful, since there is relatively little mutual deviation in the values of those varieties where the number of samples is greatest. However, a tentative calculation was made of the significance of the difference between varieties Welling- ton X and Wellington XXX, of which the former is No. 4 in the sequence, and the latter No. 10. The following result was obtained; Limits of variation Average St. D. n calculated observed Wellington X 682 ± 200 3 482-882 490-889 Wellington XXX 499 ±175 11 324-674 308-821 Degree of freedom: 12 P 80 % Thus the differences between the varieties may in fact be assumed to possess some significance, although not very much. The effect of the summer temperature was already observable in Figure 10, which shows that the colour strength was greatest when the temperature was highest. This is also indicated in the comparison of mean values of all samples for each year, presented in the following; Limits of variation Average St. D. n calculated observed 1962 574 ± 147 16 427-721 380-988 1963 715 ± 175 16 540-890 410-930 1964 430 ± 130 20 300-560 282-810 Degree of freedom P Difference between 1962-1963 30 95% » » 1963-1964 34 99% Fig. 10. Colour strength of black-currant varieties in the different years investigated, compared with the average. # 299 Thus in 1963, when the summer was warmest, the colour strength was signif- icantly greater than in both the other summers. Against this, the warm summer diminished the dry matter, so that the greater colour strength is not connected with increased dry matter; even if the summer temperature is high, the water con- tent of these berries is not diminished, by virtue of the protecting wax coating of the berry surface; the loss of dry matter again is probably attributable to increased metabolism caused by higher temperature. An increase of colour strength may be connected with the fact that high temperature (or abundant sunshine) favours the synthesis of anthocyanins: it might also be that in a warm summer the berries remain smaller than in a cool one, whereby the relative proportion of the skin is increased; the anthocyanins are localized in the skin part. The size of the berries was measured only in 1964, by weighing 100 of them. This material was used as a basis for a study of the correlation between the size of the berries and the colour strength, as shown in Fig. 11. Is seems that a slight negative correlation is observable. In the figure, the effect of variety and the locality of growing are detectable. No very clear-cut differences are present. Strong colour is observable in Wellington X; in Brödtorp, the colour is stronger than in Wellington XXX and Black of Lepaa. It seems, as regards the various localities, that berries from Piikkiö are large, those from Pälkäne and Laukaa again relatively small. Furthermore, in 1962, although the size was not measured, Boskoop was observed Fig. 11. Correlation between the berry size and colour strength according to results obtained in 1964. 300 to be a particularly small-sized berry, and correspondingly the colour was very strong. It is regrettable that the berry size was not measured in 1962 and 1963, as it is not possible to establish whether high summer temperature had reduced the berry size. A study may also be made whether a more southern latitude of the growing locality has an effect corresponding to high summer temperature. For this purpose, the averages of all samples for each locality have been compared. This comparison is presented below. Piikkiö Pälkäne Laukaa Ylistaro Maaninka Rovaniemi Average n Limits of variation 626 21 282-988 660 5 438-810 591 7 344-890 411 6 308-531 484 10 317-716 450 3 410-499 It can be seen that a slightly increasing trend towards the south occurs, although this is not very clear-cut. However, there is no increase to be found between Pälkäne and Piikkiö, and the values for Ylistaro are low (in this case, changes attributable to transport were perhaps partly responsible). A very marked influence of the degree of southern latitude is, in fact, not to be expected, since the local micro-climate may here as well signify more than the actual latitude of the place. The possible effect of the amount of sunshine can also be considered on the basis of the present material. It has been established that light is essential for the formation of anthocyanins (cf. 7), and thus a study was made whether a correlation exists between the colour strength and the corresponding totals of hours of sunshine, or cumulative totals of heat. In this connexion it was found that there existed a comparatively clear correlation with respect to the totals of heat; in the case of hours of sunshine, some correlation was also present, although it was less distinct. In both cases, the type of deviation led to the assumption that from some point onwards increasing heat or light no longer increased the colour strength. It is prob- able that light in particular was in excess, so that it did not form a limiting factor. Literature contains relatively little information concerning the colour strength of black-currant varieties. Baumann (3), when comparing different varieties, mentions that differences between the varieties are inessential. From the point of view of quality he considers vitamin C most important, and as regards cultivation, also the yield. In his opinion, acid content, colour strength and aroma are less im- portant, and accordingly no values are given for these properties. Ayres, Charley & Swindells (1) give some values for juices pressed from different varieties, and show that colour strength is lowest for early crop, higher in the middle of season, and even somewhat higher in the late season. Of the varieties studied, only a few were the same as here; thus the colour strength of Wellington XXX was greater than of Westwick Choice, which agrees with the average obtained here (it is true that the difference is only slight, and in 1962 the result is the reverse). Koch & Bretthauer (16) found the amount of anthocyanins in Boskoop and Silvergieter 301 Table 9. Formol values of black-currant varieties during the 3 years, and the general averages. 1962 1963 1964 Average Westwick Choice 24 24 Black of Lepaa 20 24 19 21 Wellington XXX 18 17 17 17 Brödtorp 15 16.5 17.5 16 Roodknop 16 16 Boskoop 16 16 Silvergieter 14 14 - 14 Äström 14 14 Goliath 14 11.5 11 12 Gerby 14 - 9 12 Janslunda 18 1 9 9 Wellington X 12 2.5 11 8.5 to be greater than in Roodknop and Wellington 30, a result which resembles that obtained here. Gleisberg & Aumann (8) report for black-currant (variety Silver- gieter) 76.0 mg anthocyanin/100 ml as colour strength; however, it is difficult to compare this finding with the present results. Formol value Table 9 presents the averages of varieties during the 3 years, the general aver- ages being arranged in their diminishing order. Some of the assays were made with fresh berries, and in part frozen material was used. Fig. 12. Formol value of black-currant varieties in the different years investigated, compared with the averages. 302 Fig. 12 illustrates the results. It can be observed that for most of the varieties the differences between the years are rather small, the effect of the different years being very slight is seen only in the fact that some exceptionally low values were noted in 1963. This might be connected with formol values being high in unripe berries (cf. 26); thus the berries would be most definitely ripe in 1963, when the temperature was high. It general, however, the values are higher than those for 1963, remaining in the range 8—24. Wyler (26) gives for black-currant the values 25 (unripe) and 20 (ripe). Other literature values are found in Ayres, Charley & Swindells (1): for early crop 13.75, middle season 17.2 and late season 16.82. As regards the varieties corresponding to those here, there are Wellington XXX: 14.9, and Westwick Choice: 21.05. The order is the same as here, although the British values are somewhat lower than the present ones. A comparison of the averages of the different years is shown below. 1962 1963 1964 All together No. 17 16 21 54 Average 16.5 15.0 16.1 15.9 Limits of variation 12 —24 1— 33 9 25 1 —33 In 1962, which was the coolest year, the average was the highest, and in 1963, which was the warmest, the average was the lowest, although the difference is not very great. Correspondingly, the values for the different localities are given in the following: n Average Limits of variation Piikkiö 21 15.2 1-33 Pälkäne 5 12.7 8-19 Laukaa 7 16.9 14-20 Ylistaro 6 14.7 9-19 Maaninka 11 17.1 11.5-25 Rovaniemi 4 20.5 16 25 In the values, a slightly increasing tendency towards the north is noted, prob- ably connected with the slower achievement of maturity there. On the other hand, low formol values may indicate overripeness, and possible changes induced by adverse transport conditions. Summary The quality properties of black-currant have been investigated in respect of 12 home-grown varieties. Samples were obtained from 6 localities over a period of 3 years. The properties studied were dry matter, pectin and its degree of ester- ification, acid content, colour strength, and formol value. As regards dry matter, the differences between the varieties were small. A high summer temperature diminished the dry matter values. Some variations existed between the varieties in respect of pectin. Thus Wel- lington XXX and X contained an abundant amount of pectin, whereas Brödtorp 303 and Black of Lepaa contained little. A high summer temperature lowered the pectin content, but the degree of its esterification remained high. A corresponding effect was noted as a consequence of the degree of north latitude of the place of growth: the amount of pectin was increased and its degree of esterification was lowered towards the north. With respect to the acid content, differences were remarked among the varieties, corresponding approximately to results reported earlier in literature. As a rule, the acid content of the home-grown varieties is higher than the values so reported. Of weather factors, sunshine seems to exercise most influence on the acid content, the acid being increased by a lack of it. Similarly, differences among the varieties were found in colour strength. This property seems to bear a negative correlation to the berry size, since the colouring compounds are localized in the skin part of the berry. The colour strength depends markedly upon the summer temperature, as is evidenced by both the comparison of the different years, and that of the different localities. Slight differences in the formed value were notedbetween the varieties. However, this value depends substantially upon the degree of maturity; it falls during ripening, a fact which renders comparison difficult. REFERENCES (1) Ayres, A. D., Charley, V. L. S. & Swindells, R. 1961. The chemical composition of some British blackcurrants. 2. Detailed evaluation of blackcurrant juices. Food Proc. & Packag. 30: 413 - 422. (2) Baumann, J. 1956. Der Einfluss der Rohware auf die Qualität der Fruchtsäfte. Beeren- und Stein- obst. IV. Internal. Fruchtsaft-Kongress 28. 5. 2. 6. 1956. Stuttgart Höhenpark Killes- berg. Kongress-Vorbericht: 100 106. (3) —1960. Die schwarze Johannisbeere 1960. Fliiss. Obst 27, 9: 5 19. (4) Biale, J. 8., 1964. Growth, maturation, and senescence in fruits. Science 146: 880 888. (5) Bogdanski, K., Zalewski, W. & Bogdanska, H. 1956. Studies on the 1-ascorbic acid content, color and certain other components and properties of black currant varieties. Roczniki Nauk Rolniczych(A), 73. 123 - 143, (6) Fink-Ullepitsch, W. 1961. Zur Qualitätsbeurteilung schwarzer Johannisbeer-Muttersäfte. Fruchtsaft-Ind. 6, 5 -6: 205 207, (7) Gee, M., McComb, E. A. & McCready, R. M. 1958. Characterization of pectic substances in fruit and sugar beet marcs. Food Res. 23: 72 75. (8) Gleisberg, W. & Aumann, H. 1958. Die Flavonole der Schwarzen Johannisbeere. I. Der Gehalt der Beeren an Flavonolen. Gartenb.wiss. 23, (5), 4: 512 531. (9) Gomolyako, L. G. 1961. Biochemical properties of currant crops in the extreme north. Ref. Chem. Abstr. 55; 25, 26300 i. (10) Gouny, P. & Vangheesdaele, G. 1960. Observations sur I’evolution biochimique des fruits de cassis au cours de leur developpemcnt. Ann. Physiol. Veg. 2: 269 279. (11) Groven, I. 1962. Sortsforsog med solbaer. Tidskr, for Planteavl 65:411 434. (12) Heun, E. 1951. Die Rohsafte-Kur. Stuttgart. (13) Jacobs, M. B. 1938. Chemical analysis of foods and food products. New York. (14) Kertesz, Z. I. 1951. The pectic substances. New York London. (15) Kieser, M, E., Pollard, A. & Sissons, D. J. 1957. The activity of pectin methylesterase in black currants. Progress Kept. Ann. Kept. Long Ashton Research Sta. 134 137. 304 (16) Koch, J. & Bretthauer, G. 1958. Untersuchungen zur Herstellungsvereinfachung und Qualitäts- verbesserung der Beerensiissmoste. Fruchtsaftind. 3: 97 112. (17) Koch, J. & Zeyen, E. 1957. Standardization of black currant juice products by means of chemical analysis, Ibid. 2: 121 127. (18) Kuusi, T. 1965. The most important quality criteria of some home-grown black-currant varieties. I. Ascorbic acid. J. Sci. Agr. Soc. Finland 38: 264 281. (19) Maurer, K. J. 1957. Fliiss. Obst 24: 11. (20) McCready, R. M. & McComb, E. A, 1952. Extraction and determination of total pectic materials in fruits. Anal. Chem. 24, 12: 1986 1988. (21) Nehring, P, & Krause, H. 1958. Konserventechnisches Taschenbuch der Obst- und Gemiise- verwertungsindustrie. Braunschweig. (22) Official methods of analysis of the association of official agricultural chemists, 9 ed. Washington 1960. (23) Souci, S. W., Fachmann, W. & Kraut, H. 1962. Die Zusammensetzung der Lebensmittel. Nähr- wert-Tabellen. Stuttgart, (24) Tressler, D. K. & Joslyn, M. A. 1961. Fruit and vegetable juice processing technology, West- port, Connecticut. Pp. 713 729: Black currant juice products, by V. L. S. Charley. (25) Turpeinen, O. & Roine, P. 1960. Ruoka-ainetaulukko. Helsinki (Keuruu). (26) Wyler, O. 1955. Formolzahlbestimmung auf potentiometrischem Wege. Mitt. Lebensm. u. Hyg. 46, 6: 515 - 524. SELOSTUS: MUSTAHERUKAN TÄRKEIMMISTÄ LAATUOMINAISUUKSISTA ERÄILLÄ KOTIMAASSA VILJELLYILLÄ LAJIKKEILLA 11. Kuiva-aine, pektiini, happopitoisuus, väri ja formoliarvo. Taina Kuusi Valtion teknillinen tutkimuslaitos, Elintarviketeollisuuslaboratorio, Otaniemi Mustaherukan laatuominaisuuksia tutkittiin 12 kotimaassa viljellyllä lajikkeella; näytteitä saa- tiin 6 eri paikkakunnalta 3 vuoden aikana. Tutkimuksen kohteina oli kuiva-aine, pektiini ja sen esteröi- tymisaste, happopitoisuus, värinvoimakkuus ja formoliarvo. Kuiva-aineeseen nähden lajikkeet poikkesivat toisistaan melko vähän. Korkea kesälämpötila vaikutti kuiva-ainetta alentavasti. Pektiiniin nähden esiintyi jonkin verran eroja eri lajikkeiden välillä; mm. Wellingtonit sisälsivät runsaasti pektiiniä, Brödtorp ja Lepaan musta taas vähän. Korkea kesälämpötila alensi pektiinin määrää, mutta esteröitymisaste oli tällöin korkea. Vastaava vaikutus olikasvatuspaikan pohjoisuudella: pektiinin määrä suureni ja sen esteröitymisaste aleni pohjoiseen päin. Happopitoisuuteen nähden esiintyi lajikkeiden kesken eroja, jotka suunnilleen vastaavat kir- jallisuudessa aikaisemmin esitettyjä. Hapon määrä oli kotimaisilla lajikkeilla korkeahko kirjallisuuteen verrattuna. Sääolosuhteista vaikuttanee happopitoisuuteen eniten aurinkoisuus siten, että auringon- paisteen puute suurentaa happomäärää. Värinvoimakkuuteen nähden esiintyy samoin lajikkeiden keskisiä eroja. Värinvoimakkuus lienee negatiivisessa korrelaatiossa marjan kokoon, koska väriaineet ovat marjan kuoriosaan lokalisoituneet. Värinvoimakkuus on kesän lämpötilasta suuresti riippuvainen. Tämä ilmenee sekä eri vuosien että eri paikkakuntien vertailusta. Formoliarvossa esiintyy vähäisiä eroja eri lajikkeiden välillä. Fonnoliarvo on kuitenkin suuresti kypsyysasteesta riippuvainen alentuen kypsymisen aikana, mikä vaikeuttaa vertailua.