DOI: https://doi.org/10.4316/fens.2023.023 248 Journal homepage: www.fia.usv.ro/fiajournal Journal of Faculty of Food Engineering, Ştefan cel Mare University of Suceava, Romania Volume XXII, Issue 4 - 2023, pag. 248 - 254 EFFECT OF HEAT PROCESSING ON VITAMIN COMPOSITION OF SELECTED STAPLE GREEN LEAFY VEGETABLES IN NIGERIA *Sunday Adegoke ADENIYI 1, Peter Agbomire AGBUGUI 1, Saheed Olanrewaju Abiodun SOLOLA 1, Jacob Sunday OYEKU 2 1Department of Chemistry, College of Natural and Applied Sciences, Igbinedion University, Okada, Edo State, Nigeria, gokeomen@gmail.com 2Department of Industrial Chemistry, College of Natural and Applied Sciences, Igbinedion University, Okada, Edo State, Nigeria. *Corresponding author Received 25th October 2023, accepted 28th December 2023 Abstract: This study assessed the effect of the steamed and boiling cooking methods on the vitamin content of six staple green vegetables in Nigeria. Vitamin levels in fresh, steamed and boiled leafy vegetables were determined using spectrophotometric and titrimetric methods. The results of vitamin analysis showed that fresh vegetable of Amaranthus hybridus contained the largest amount of ascorbic acid, thiamin and niacin (358.40 mg/100 g, 0.09 mg/100 g and 0.08 mg/100 g), while Talinum triangulare had the highest level of riboflavin (0.18 mg/100 g). The steamed Amaranthus hybridus contained the highest levels of ascorbic acid, thiamin and niacin (322.56 mg/100 g, 0.08 mg/100 g and 0.73 mg/100 g), while steamed leaves of Talinum triangulare had the highest quantity of riboflavin (0.16 mg/100 g). The boiled Amaranthus hybridus had the highest amount of ascorbic acid, thiamin and niacin (197.12 mg/100 g, 0.05 mg/100 g and 0.41 mg/100 g), whereas the boiled Talinum triangulare had the highest level of riboflavin (0.09 mg/100 g). The percentage of vitamin loss in steamed leafy vegetables varies from 9 to 11 %, 9 to 17 %, 9 to 13 % and 9 to 12 % in ascorbic acid, thiamin, riboflavin and niacin respectively. Almost 50 % of the essential vitamins were lost in boiled leafy vegetables. The results revealed that vegetables could be improved source of some important vitamins that can help humans meet their nutritional needs. Keywords: Leafy vegetables, Steaming/Boiling methods, Vitamin composition, % loss of vitamin 1. Introduction Generally, herbaceous plants’ fresh and edible parts are known as green vegetables. They are a great source of important vitamins [1]. Leafy vegetables contain beneficial ingredients in food which serve as energy sources and also possible to be utilized as body building, regulatory and protection. Leafy vegetables have become regular ingredient in the daily diet of Nigerians in both urban and rural areas because they are readily available and affordable. Leafy vegetables can be consumed raw or cooked, and the majority of their vitamins are water-soluble and heat- sensitive. According to reports, when the leafy vegetables are soaked in hot water, these water-soluble vitamins might drain away [2]. Nevertheless, these leafy vegetables are commonly exposed to various cooking processes in order to increase their palatability [3]. They are extremely vulnerable to vitamins loss during processing [4], hence the contents of water- soluble vitamins can be altered by most of these processing methods, particularly the thermolabile components, thereby reducing the amount of the water-soluble vitamins http://www.fia.usv.ro/fiajournal mailto:gokeomen@gmail.com Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXII, Issue 4 – 2023 Sunday Adegoke ADENIYI, Peter Agbomire AGBUGUI, Saheed Olanrewaju Abiodun SOLOLA, Jacob Sunday OYEKU, Effect of heat processing on vitamin composition of selected staple green leafy vegetables in Nigeria, Food and Environment Safety, Volume XXII, Issue 4– 2023, pag 248 – 254 249 required for daily body metabolism [5]. Therefore, this study evaluates and compares the vitamin content and retention in six regularly consumed vegetable species, namely, Amaranthus hybridus, Corchorus olitorius, Ocimum gratissimum, Talinum triangulare, Telfaria occidentalis and Vernonia amygdalina, both fresh and processed, in order to acquire the necessary vitamins, like, ascorbic acid (vitamin C), thiamin (vitamin B1), riboflavin (vitamin B2) and niacin (vitamin B3) that are important for human metabolism and protection of human body against diseases. Table 1 lists the local names, botanical names, common names and portions of the plant that were used. Table 1. Staple Leafy Vegetables, names and parts used Local name Botanical name Common name Part used Tete Amaranthus hybridus African spinach Leaves Ewedu Corchorus olitorius Jute plant Leaves Efinrin-nla Ocimum gratissimum Basil Leaves Gbure Talinum triangulare Water lettuce Leaves Ugwu Telfaria occidentalis Fluted pumpkin Leaves Ewuro Vernonia amygdalina Bitter leaf Leaves 2. Materials and Methods Reagents Chemicals and solvents of analytical grade were utilized without additional purification. Ethanol, and petroleum ether, concentrated sulphuric acid and hydrochloric acid were obtained from BDH Chemicals, England, while trichloroacetic acid was obtained from E. Merck, Germany. Plant Material Fresh leaves of the six vegetables were bought in the market at Okada, Edo State, Nigeria. The identification and authentication of the plant leaves were carried out at the Taxonomy section, Biological Sciences Department, Igbinedion University, Okada, Nigeria. Sample Preparation Each sample was completely mixed, the stalks were removed and de-ionized water was used to rinse the samples, which was evaporated at ambient temperature. The residual moisture was evaporated during air-drying process that took place for few weeks on a clean paper with regular turning over to avoid fungal growth. Using pestle and mortar, each air-dried sample was crushed into a fine powder and sieved through a 2.0 mm mesh sieve [6]. Thermal Processing Also, thermal processing (steaming and boiling) of the samples fresh leaves was carried out following the procedure described by Soni and Brightwell [7] with minor modification. Steaming 5 g each of fresh vegetable leaves were cooked in a clean stainless-steel pot using an electric cooker, fitted with temperature control for 10 minutes. After that, the sample was immersed in a water bath at 4ºC for 30 seconds to stop cooking. Excess water was further removed with desiccant paper. The steamed leaves were air-dried for few weeks on a clean paper with regular turning over to avoid fungal growth. Pestle and mortar were used to crush each air- dried sample into a fine powder, sieved Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXII, Issue 4 – 2023 Sunday Adegoke ADENIYI, Peter Agbomire AGBUGUI, Saheed Olanrewaju Abiodun SOLOLA, Jacob Sunday OYEKU, Effect of heat processing on vitamin composition of selected staple green leafy vegetables in Nigeria, Food and Environment Safety, Volume XXII, Issue 4– 2023, pag 248 – 254 250 through a 2.0 mm mesh sieve and stored in an air tight container for subsequent use [7]. Boiling 5 g each of fresh vegetable leaves were cooked with distilled water that was brought to boiling for 10 minutes with the lid on. The vegetables were sieved and left to cool at ambient temperature after boiling. Pestle and mortar were used to crush each air-dried sample into a fine powder, sieved through a 2.0 mm mesh sieve and stored in an air tight container for subsequent use [7]. Vitamin Analysis Ascorbic acid (Vitamin C) In an extraction tube, 5.0 g of the sample was weighed, along with 100 mL of EDTA/TCA (2:1). The extracting solution was combined and shook for 30 minutes before being transferred to a centrifuge tube and centrifuged for roughly 20 minutes at 3000 rpm. The extracting solution was then transferred to a 100 mL volumetric flask and made up to 100 mL mark. 1% starch indicator was added to 20 mL of extract pipetted into a volumetric flask. To obtain a dark end point, these were added and titration was done using a 20% CuSO4 solution [8]. Thiamin (Vitamin B1) A total of 5.0 g of the sample was homogenized in 50 mL of ethanolic sodium hydroxide and filtered into a 100 mL flask. 10 mL of the filtrate was pipetted into a 100 mL flask, along with 10 mL of potassium dichromate to develop the colour and the results were read at 360 nm. At the same wavelength, a blank sample was prepared and the colour was established and read [9]. Riboflavin (Vitamin B2) 100 mL of 50% ethanol solution was used to extract 5.0 g of the sample, which was agitated for 1 hour. It was filtered into a 100 mL flask, and 10 mL of the extract was pipetted into a 50 mL volumetric flask. 10 mL of potassium permanganate (5%) and 10 mL of H2O2 (30%) were added and allowed to stand for 30 minutes over a hot water bath. Thereafter, 2 mL of sodium sulphate (40%) was added, made up to 50 mL mark and the absorbance was measured in a spectrophotometer at 510 nm [9]. Niacin (Vitamin B3) 50 mL of 1 N sulphuric acid was added to 5.0 g of the sample and agitated for 30 minutes. The sample was filtered after 3 drops of ammonia solution was added. 10 mL of the filtrate were transferred into a 50 mL volumetric flask, then 5 mL potassium cyanide were added. This was acidified with 5 mL of 0.02 N H2SO4 and the absorbance was measured with the spectrophotometer at 470 nm [9]. Statistical analysis For each parameter, a triplicate study was performed on each independent replication. Each treatment had three independent replicates (n = 3), with the data displayed tables and expressed as means ± standard deviation (SD). Data were analyzed by ANOVA (P < 0.05). 3. Results and Discussion Vitamin composition of fresh and processed leafy vegetables Table 2a-2c summarizes the evaluated values of fresh, steamed and boiled vegetables. All fresh steamed and boiled green vegetables are particularly high in vitamins, according to the results of the vitamin analysis. For both fresh and steamed leafy vegetables, ascorbic acid (vitamin C) ranges from 358.40 mg/100 g to 215.63 mg/100 g and 322.56 mg/100 g to 191.91 mg/100 g in A. hybridus to T. triangulare respectively, but for boiled leafy vegetables, it ranges from 179.12 Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXII, Issue 4 – 2023 Sunday Adegoke ADENIYI, Peter Agbomire AGBUGUI, Saheed Olanrewaju Abiodun SOLOLA, Jacob Sunday OYEKU, Effect of heat processing on vitamin composition of selected staple green leafy vegetables in Nigeria, Food and Environment Safety, Volume XXII, Issue 4– 2023, pag 248 – 254 251 mg/100 g in A. hybridus to 95.94 mg/100 g in O. gratissimum. For both fresh and steamed leafy vegetables, thiamin (vitamin B1) ranges from 0.09 mg/100 g to 0.03 mg/100 g in A. hybridus to O. gratissimum, whereas for boiled leafy vegetables, it ranges from 0.05 mg/100 g in A. hybridus to 0.02 mg/100 g in C. olitorius. For fresh, steamed and boiled leafy vegetables, riboflavin (vitamin B2) levels range from 0.18mg/100 g to 0.06mg/100 g, 0.16 mg/100 g to 0.05 mg/100 g and 0.09 mg/100 g to 0.03 mg/100 g in T. triangulare to C. olitorius respectively. Niacin (vitamin B3) levels in fresh, steamed and boiled leafy vegetables range from 0.80 mg/100 g to 0.29 mg/100 g, 0.73 mg/100 g to 0.26 mg/100 g and 0.40 mg/100 g to 0.15 mg/100 g in A. hybridus to O. gratissimum respectively. Table 2a. Vitamin composition of fresh leafy vegetables on mg/100 g dry weight Vegetable Vitamin Ascorbic acid Thiamin Riboflavin Niacin Amaranthus hybridus 358.40 ± 0.20 0.09 ± 0.01 0.12 ± 0.01 0.80 ± 0.01 Corchorus olitorius 316.80 ± 0.22 0.03 ± 0.01 0.06 ± 0.01 0.61 ± 0.02 Ocimum gratissimum 241.06 ± 0.21 0.03 ± 0.02 0.08 ± 0.02 0.29 ± 0.01 Talinum triangulare 215.63 ± 0.11 0.06 ± 0.01 0.18 ± 0.02 0.56 ± 0.02 Telfaria occidentalis 356.11 ± 0.20 0.07 ± 0.01 0.09 ± 0.01 0.74 ± 0.01 Vernonia amygdalina 285.92 ± 0.21 0.06 ± 0.01 0. 07 ± 0.01 0.66 ± 0.01 Results are mean of triplicate determinations on a dry weight basis ± standard deviation. Table 2b. Vitamin composition of steamed leafy vegetables on mg/100 g dry weight Vegetable Vitamin Ascorbic acid Thiamin Riboflavin Niacin Amaranthus hybridus 322.56 ± 0.11 0.08 ± 0.02 0.11 ± 0.01 0.73 ± 0.01 Corchorus olitorius 288.29 ± 0.21 0.03 ± 0.02 0.05 ± 0.01 0.54 ± 0.02 Ocimum gratissimum 216.95 ± 0.18 0.02 ± 0.01 0.07 ± 0.02 0.26 ± 0.01 Talinum triangulare 191.91 ± 0.12 0.05 ± 0.02 0.16 ± 0.02 0.50 ± 0.02 Telfaria occidentalis 316.94 ± 0.21 0.06 ± 0.02 0.08 ± 0.01 0.65 ± 0.01 Vernonia amygdalina 257.33 ± 0.20 0.05 ± 0.01 0. 06 ± 0.01 0.60 ± 0.01 Results are mean of triplicate determinations on a dry weight basis ± standard deviation. Table 2c. Vitamin composition of boiled leafy vegetables on mg/100 g dry weight Vegetable Vitamin Ascorbic acid Thiamin Riboflavin Niacin Amaranthus hybridus 197.12 ± 0.20 0.05 ± 0.01 0.06 ± 0.01 0.41 ± 0.02 Corchorus olitorius 158.40 ± 0.22 0.02 ± 0.01 0.03 ± 0.01 0.31 ± 0.02 Ocimum gratissimum 95.94 ± 0.21 0.02 ± 0.01 0.04 ± 0.01 0.15 ± 0.01 Talinum triangulare 107.82 ± 0.11 0.04 ± 0.01 0.09 ± 0.01 0.29 ± 0.01 Telfaria occidentalis 178.06 ± 0.20 0.04 ± 0.01 0.05 ± 0.01 0.37 ± 0.01 Vernonia amygdalina 145.82 ± 0.21 0.04 ± 0.01 0. 04 ± 0.01 0.34 ± 0.01 Results are mean of triplicate determinations on a dry weight basis ± standard deviation. The results revealed that vegetables contain significant amounts of vital vitamins with Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXII, Issue 4 – 2023 Sunday Adegoke ADENIYI, Peter Agbomire AGBUGUI, Saheed Olanrewaju Abiodun SOLOLA, Jacob Sunday OYEKU, Effect of heat processing on vitamin composition of selected staple green leafy vegetables in Nigeria, Food and Environment Safety, Volume XXII, Issue 4– 2023, pag 248 – 254 249 fresh vegetables having higher concentrations, followed by steamed vegetables and boiled vegetables having the lowest. The disparity in the vitamin levels in fresh leafy vegetables could be as a result of soil profiles in which the vegetables were planted, impacts of human activities and varied climatic factors, while that of steamed and boiled leafy vegetables could be credited to changes in analytical protocols, processing time and conditions [8, 10]. In general, leafy vegetables are high in vitamins, which are required for a variety of daily biological processes, including cell reproduction [11], growth and cellular energy processing [12]. The result of this study showed that the fresh, steamed and boiled A. hybridus had the highest quantity of ascorbic acid, thiamin and niacin, indicating that A. hybridus can be consumed on regular basis, as ascorbic acid is crucial for biosynthesizing collagen in human body [13], protein metabolism [14] and increasing the body’s resistance to infections [15, 16]. Thiamin also allows the body to use carbohydrates as energy, which it does mostly in muscles, brain, liver and kidney. It also has an impact on glucose metabolism [17]. Niacin is also essential in cells for energy transfer and to repair DNA [18]. Meanwhile, the maximum amount of riboflavin was found in the fresh, steamed and boiled T. triangulare, which is crucial for growth and overall health. It also helps the human body in breaking down carbohydrates, proteins and fats to produce energy, in addition, allowing the body to use oxygen [19, 20]. Percentage loss of vitamin composition of fresh and processed leafy vegetables The impact of heat processing on the vitamin contents of the vegetables was also investigated. Table 3a and 3b show the estimated percentage loss of vitamin composition of fresh and processed vegetables. For steamed leafy vegetables, the percentage loss of ascorbic acid varies from 9 to 11 % in C. olitorius to T. triangulare and T. occidentalis, whereas the percentage loss of ascorbic acid in boiled leafy vegetables varies from 45 to 50 % in A. hybridus, C. olitorius, T. triangulare and T. occidentalis. For steamed leafy vegetables, the percentage loss of thiamin varies from 9 to 17 % in T. occidentalis and O. gratissimum, whereas the percentage loss of thiamin in boiled leafy vegetables varies from 48 to 50 % in A. hybridus, O. gratissimum, C. olitorius, T. triangulare and V. amygdalina. For steamed leafy vegetables, the percentage loss of riboflavin varies from 9 to 13 % in T. triangulare and C. olitorius, whereas the percentage loss of riboflavin in boiled leafy vegetables varies from 49 to 50 % in C. olitorius and V. amygdalina, A. hybridus, T. triangulare, O. gratissimum and T. occidentalis. For steamed leafy vegetables, the percentage loss of niacin varies from 9 to 12 % in V. amygdalina, A. hybridus and T. occidentalis, whereas the percentage loss of niacin in boiled leafy vegetables varies from 48 to 50 % in V. amygdalina, C. olitorius, T. occidentalis and O. gratissimum. According to the findings, boiling had the most adverse impact on the vitamin content of the vegetables, accounting for nearly 50 % loss, while steaming accounted for approximately 17 % loss. This is in agreement with Oladejo’s findings [21]. To obtain the necessary daily intake of the aforementioned vitamins, we recommend that steamed vegetables rather than boiled vegetables be consumed on a regular basis. Table 3a. Percentage loss of vitamin composition of steamed leafy vegetables Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXII, Issue 4 – 2023 Sunday Adegoke ADENIYI, Peter Agbomire AGBUGUI, Saheed Olanrewaju Abiodun SOLOLA, Jacob Sunday OYEKU, Effect of heat processing on vitamin composition of selected staple green leafy vegetables in Nigeria, Food and Environment Safety, Volume XXII, Issue 4– 2023, pag 248 – 254 253 Vegetable % Loss of Vitamin Ascorbic acid Thiamin Riboflavin Niacin Amaranthus hybridus 10 11 10 9 Corchorus olitorius 9 14 13 11 Ocimum gratissimum 10 17 11 10 Talinum triangulare 11 10 9 10 Telfaria occidentalis 11 9 10 12 Vernonia amygdalina 10 11 12 9 Table 3b. Percentage loss of vitamin composition of boiled leafy vegetables Vegetable % Loss of Vitamin Ascorbic acid Thiamin Riboflavin Niacin Amaranthus hybridus 45 48 50 49 Corchorus olitorius 50 50 49 50 Ocimum gratissimum 49 48 50 50 Talinum triangulare 50 50 50 49 Telfaria occidentalis 50 49 50 50 Vernonia amygdalina 49 50 49 48 4. Conclusion The findings of this study revealed that the leafy vegetables studied are high in vitamins that are required for cell reproduction, growth and energy utilization. The study found that A. hybridus had the highest quantity of ascorbic acid, thiamin and niacin in the fresh, steamed and boiled vegetables assessed, implying that regular consumption of A. hybridus will aid during the biosynthesis of the collagen in the body and increase the body’s resistance to infections. 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