ReseaRch PaPeR Journal of Agricultural and Marine Sciences 2022, 27(1): 112–117 DOI: 10.53541/jams.vol27iss1pp112-117 Received 30 Jan 2021 Accepted 01 July 2021 Rehydration ability of native dried date (Phoenix dactylifera L.) fruits soaked in orange juice Messaid Habiba, Ait-Ameur Lamia, Benamara Salem* Benamara Salem*( ) sbenamara2001@yahoo.fr, Research Labo- ratory in Food Technology, Faculty of Engineering Sciences, University M’hamed Bougara, Boumerdès, 35000, Algeria Introduction Preservation of genetic diversity of date palm (Phoe-nix dactylifera L.) tree needs valorization of date fruits (DFs) having low commercial value (Acou- rene et al., 2007). Native dry DF varieties like Mech-De- gla are known to be a sugar-rich material, attributing to the fruit pulp a sweet taste and non-juicy consistency. Rehydration is a unit operation widely used in food pro- cessing (Amami et al., 2006). This is a complex process aimed at the restoration of the food properties, includ- ing thermophysical properties (Vega-Gálvez et al., 2009). Many works have been devoted to rehydration pro- cess of different fruits, including DFs, using distilled water as soaking media: hot air-dried DFs (Falade and Abbo, 2007), freeze-dried pineapple, mango, guava, acerola and papaya (Marques et al., 2009), softening of over dried ‘Deglet Nour’ dates and impact of rehydration on the dried products (Boubekri et al., 2010), osmotic pre-dehydrated, hot-air and microwave-vacuum dried strawberry and apples (Kowalska et al., 2018) , etc. How- ever, to our knowledge, little research has been reported on the rehydration using fruit juices as soaking media. The present paper reports on the rehydration abil- ity of Algerian native dry DFs (Phoenix dactylifra L., var. Mech-Degla) using orange juice as soaking liquid. The orange juice could add specific physicochemical, nutritional and organoleptic characteristics to new infused fruit. It is worth pointing out that the pos- sibility of obtaining dried date fruits infused in syr- up was initially reported by Amellal et al. (2007) and Benamara et al. (2008). Preservation of fruits in syr- up is well known traditional method (Tindall, 1994). (Phoenix dactylifera L.) قدرة مثار النخيل اجملفف على الرتطيب عن طريق نقعها يف عصري الربتقال مسيد حبيبة ، آيت عامر ملياء ، بن عمارة سامل Abstract. Algerian date (Phoenix dactylifera L., dried variety Mech-Degla) fruits (DFs) are of low commercial value. To our knowledge, research on the rehydration of DFs by soaking in citrus or other fruit juic- es is limited. The present paper reports on the soaking process of naturally dried DFs in orange juice (OJ). The DF rehydration ability was analyzed by applying two levels factorial design with three responses (DF weight gain, OJ °Brix and DF breaking strength) and three factors (soaking temperature “X1”, soaking time “X2” and OJ volumetric fraction “X3”). The optimal experimental conditions (X1 = 5 °C, X2 = 24 h and X3 = 0.1) allowed to achieve weight gain ~ 0.5, °brix ~ 16 °Bx and breaking strength of 0.6 N (i.e. against 3.7 N for the initial DFs). In addition, the resulting syrup-infused DFs showed a good heat treatment capability in terms of texture retention. The soaking of dried DFs in citrus juice like OJ could be an alternative to valorize such products. Keywords: Dried date fruit, orange juice, rehydration, soaking, syrup امللخص:تعتــر التمــور اجلزائريــة )Phoenix dactylifera L( مــن النوعيــة اجلافــة )Mech-Degla( ذات قيمــة جتاريــة منخفضــة. و علــى حــد علمنــا، فــإن البحــوث العلميــة يف معاجلــة )ترطيــب( التمــر عــن طريــق النقــع يف عصائــر احلمضيــات أو الفواكــه األخــرى حمــدودة. تشــر املقالــة احلاليــة إىل عمليــة نقــع هــذه التمــور اجلافــة طبيعيــا يف عصــر الرتقــال. متــت دراســة قــدرة ترطيــب التمــر مــن خــال تطبيــق التصاميــم التجريبيــة )تصميمــات عاملــة كاملــة( ذو مســتوين دون تكــرار مــع األخــذ بعــن االعتبــار لثاثــة متغــرات اتبعــة )زايدة وزن التمــر ، Brix° لعصــر الرتقــال ، وقــوة كســر X1=5( الظــروف التجريبيــة املثلــى . )»X3« نســبة عصــر الرتقــال »X2« مــدة النقــع ، »X1« التمــر( وثاثــة متغــرات مســتقلة)درجة حــرارة النقــع درجــات مئويــة ، X2 =24 ســاعة و X3 =0.1 ( مكنــت بتحقيــق زايدة يف وزن التمــر تقــدر ابلنصــف ، قيمــة brix ~ 16° درجــة وقــوة االنكســار N 0.6 ) مقابــل N 3.7 للتمــور الغــر معاجلــة(. ابإلضافــة إىل ذلــك، فقــد أظهــرت التمــور املشــبعة ابلعصــر قــدرة جيــدة علــى املعاجلــة احلراريــة مــن حيــث االحتفــاظ ابمللمــس. ميكــن أن يكــون اذن نقــع التمــور اجملففــة يف عصــر احلمضيــات مثــل عصــر الرتقــال بديــًا لتثمــن هــذه التمــور. الكلمات املفتاحية: التمور اجلافة، عصر الرتقال، النقع، شراب مركز، تصميمات عاملة كاملة دون تكرار. 112 SQU Journal of Agricultural and Marine Sciences, 2022, Volume 27, Issue 1 Rehydration ability of native dried date (Phoenix dactylifera L.) fruits soaked in orange juice Materials and methods Plant Materials Algerian date (Phoenix dacylifera L., dried variety Mech-Degla) fruits (DFs) were harvested in the region of Biskra (south-eastern Algeria) and purchased from the city of Constantine (north-eastern Algeria). They were characterized by high sugar content of 64% (wb), low water content of 14% (wb) and relatively high pH of 6.3 as already highlighted by Noui (2007) and Messaid (2008). These are the three most important parameters because they are likely to have a direct influence on the mass transfer and texture. The fruits were sorted and cleaned, then packaged in a polyethylene bag at 6 °C. Be- fore rehydration, the fruits were washed, dried by absor- bent paper and then cut longitudinally into two halves. The orange juice (OJ) used as soaking media was from fruits of late variety Valencia cultivated in the region of Blida (50 km west of Algiers). The oranges were cleaned, washed and dried by absorbent paper. The OJ was ex- tracted immediately prior to use, by manual pressing of orange halves using lemon squeezers. After extraction, OJ was filtrated and centrifuged. Rehydration by Soaking in Orange Juice The rehydration of DFs by soaking in diluted OJ was studied using two-level full factorial design as described by Goupy (1996). For this, three factors (variables) were considered, namely temperature of OJ used as soaking media (X1, level (-) = 5 °C and level (+) = 45 °C), soaking time (X2, level (-) = 0.5 h and level (+) = 24 h) and vol- umetric fraction of OJ in the soaking aqueous solution (i.e. mixture of distilled water and natural OJ) (X3, level (-) = 0.1 and level (+) = 0.9). The temperature was con- trolled using a refrigerator equipped with a thermostat (i.e. 5° C) and a thermostatically controlled water bath (i.e. 45° C). Three responses were taken into account, namely, DF weight gain (weight fraction, with reference to the initial weight), OJ °Brix and DF breaking strength (N). The DF halves:soaking OJ ratio was 1:3 (w/v), cor- responding to 20 g date pieces/60 mL diluted OJ. Data modeling was performed using XLSTAT software. Instrumental Texture Analysis It is well established that the texture of foods, togeth- er with color and flavor, is one of the most important quality criteria, which determines the consumer accept- ability (Andrés-Bello and Barreto-Palacios, 2013). The measurement of the breaking force (expressed in N) was carried out on DFs before and after soaking, using the texture analyzer TA Lloyd (AR2000 TA plus LLOYD instrument, Ametek, UK) with drip tray. Fundamental- ly, it consisted of three modules, namely drive system, test cell and force measuring and recording system. The plunger used was cylindrical shape with a flat base 12.7 mm in diameter, moving with a speed of 1 mm/s. Sev- eral parameters were measured but only the breaking strength, indicative of the DF firmness, is presented. For comparison purpose, commercial syrup-infused pine- apple and papaya were subjected to the same analysis. Pasteurization This test consisted essentially to check the ability of the processed date fruits to maintain texture during thermal pasteurization. Preliminary, time needed to reach the desired temperature at the center of DF pieces was de- termined, using a thermocouple (type J Blindi), a heat generator (Lauda type) and a temperature recorder (Type Servogor 210/Goerz). The DFs soaked in the OJ syrup were packaged in a glass jar, which was first sealed with a screw cap and then immersed in a thermostatical- ly controlled heating bath. The pasteurization tempera- ture was kept constant at 78 °C during pre-determined heating time of 4 min. Results and Discussion The results of rehydration ability are summarized in Ta- ble 1. As it can be seen from the table, the test 3 was the most interesting based on: i) the maximum date fruit (DF) weight gain ~ 0.5, ii) Brix value ~ 16 °Bx, corre- sponding to a syrup of light type (FAO, 2003), and iii) appreciated DF texture with a tensile strength of 0.64 N (against 3.66 ± 0.6 N for the initial fruits) (i.e. close to that of commercial syrup infused fruits, 0.63 and 1.2 N for papaya and pineapple, respectively). The breaking force of 0.64 N was chosen because among all the values obtained for the breaking force, it was the closest to 0.63 N (i.e. commercial infused papaya). None of the values did show as close to the firmness (1.2 N) of pineapple (i.e. commercial infused fruit). To our knowledge, there was negligible numerical data on the firmness of other infused fruit species. Regarding DFs, soft and chewy moist fruits are commonly preferred (Barreveld, 1993). Globally, the rehydration ability and firmness of pro- cessed DFs seemed to be close to those (2-50% and 0.4 to 2 N, respectively) of infused blueberries (Rodrigues et al., 2015). Infused fruits generally refer to the process of osmotic dehydration. In this present work, the process of soaking of DFs in orange juice (OJ) was visualized as compared to other two processes of rehydration and os- motic dehydration (Figure 1). The observed enhancement in the texture of rehy- drated DF pieces can be attributed to absorbed water (Stanley and Aguilera, 1985). In addition, various sub- strates, ions and enzymes in OJ can interact with DFs during soaking and heat treatment (Andrés-Bello and Barreto-Palacios, 2013). The color change may also be influenced by the pH value (Andrés-Bello and Bar- reto-Palacios, 2013). The rehydration ability of DF va- rieties can be depended on sun-drying of fruits on the tree. Such drying is relatively different from post-harvest drying. In fact, the high temperature of drying involves 113Research Paper Messaid, Ait-Ameur, Benamara a more rigid structure, which can lead to a lower rehy- dration rate (Ramallo and Mascheroni, 2012). Models obtained with the coded variables are given as follows, using XLSTAT software (Goupy, 1996): Weight gain: Y = 0.357 + 0.010X1 + 0.146X2 + 0.007X3 (1) °Brix : Y = 15.19 + 1.50X1 + 6.55X2 + 3.40X3 + 1.18X1X2 +0.35X1X3 – 0.40 X2X3 + 0.23X1X2X3 (2) Breaking strength: Y = 1.37 – 0.35X1 – 0.835X2 + 0.08X3 + 0.13X1X2 (3) The measured and predicted values are shown in Figure 2. For the “weight gain” response (Eq. 1), the factor time Table 1. Experimental design related to soaking of native dried dates soaked in orange juice No X1 X2 X3 Weight gain °Brix* Breaking strength, N 1 - - - 0.211 4.63 2.58 2 + - - 0.224 5.03 1.63 3 - + - 0.499 16.63 0.64 4 + + - 0.521 20.83 0.28 5 - - + 0.195 12.00 2.78 6 + - + 0.215 12.90 1.81 7 - + + 0.483 21.50 0.86 8 + + + 0.507 28.00 0.35 Level (-) 5°C ±3 0.5 h 0.1** Level (+) 45 °±3 24 h 0.9*** * Expressed as fraction, based on the initial weight; **10 % (V/V) pure orange juice; ***90 % (V/V) pure orange juice; X1: temperature of soaking juice; X2: soaking time, and X3: volumetric fraction of orange juice. Figure 1. Diagrams of rehydration in water (a), osmotic dehydration (b), and soaking date fruit in orange juice (c). The arrows of different sizes indicate the direction and, for general guidance, the intensity of the corresponding mass transfers. 114 SQU Journal of Agricultural and Marine Sciences, 2022, Volume 27, Issue 1 Rehydration ability of native dried date (Phoenix dactylifera L.) fruits soaked in orange juice (X2) has a positive main effect and it seems to be the most influential factor. In the case of “°Brix” (Eq. 2), time and OJ concentration have a positive effect and both fac- tors seem to be more influential than temperature. Re- garding the “Breaking strength” (Eq. 3), the soaking time and temperature have a negative main effect and they seem to be more influential as compared to the OJ con- centration. Moreover, there is a synergistic interaction between orange juice temperature and soaking time. The internal and external surface of DF halves at different stages of treatment are shown in the Figure 3. Sugars as essential components of DFs promote water uptake by plant tissue, whereas the fruit minerals could improve the texture firmness of the final product, and potassium being frequently associated with the fruit firmness (Guedes et al., 2013; Cromey, 2012; Watson and Lom, 2008; Neumann 1972). It should be noted that pre- liminary tests showed that the rehydration of dried DFs Figure 2. Predicted by the model and measured values of weight gain (a), °Brix (b) and breaking strength (c), (See Table 1 for units). 115Research Paper Messaid, Ait-Ameur, Benamara by soaking in water was not convenient because of the disintegration of the fruit texture (results not presented here), whereas the citrus juices produced a firm texture. Conclusion Naturally dry date fruits (DFs) showed a good ability to rehydration when they were soaked in orange juice. In addition, the thermal pasteurization improved the re- hydration ability and surface structure of infused DFs. 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