Abstract: Background and Objective: The use of soy as food ingredient has recently grown in food industry as a result of its health benefits, technological and functional properties. The objective of the research was to prepare functional products of spreadable tofu. Materials and Methods: Six formulated spreadable tofu with different flavors were prepared: Control without addition and with chopped green olives, ground black pepper+chopped green peppers, sugar, guava pulp and peach pulp. The spreadable tofu blends were subjected to chemical, physiological, microbiological and sensory evaluation to ensure different qualities. Results: Results demonstrated slight differences among treatments within the ranges of moisture, protein, fat, ash and carbohydrates. The antioxidants’ activities varied from 66.98-80.80%. Total isoflavones fluctuated between 2181 and 3259 μg g–1. All products were high in genistein, daidzein and low in isoformntine, biochainine. The highest percentages of phenolic compounds were ellagic, benzoic, catechin, pyrogallol, ferulic, naringin, hesperidin, quercetrin, naringenin and hesperetin. Among flavonoid compounds naringin, hesperidin, quercetrin , naringenin and hesperetin were scored as the highest values in tofu blends. All blends showed acceptable physicochemical properties. Fat separation was increased with extending storage period. Control spreadable tofu was less acceptable than the other blends. The microbiological investigation assured the safety of the blends. Conclusion: The present investigation confirmed that the formulated tofu blends exhibited high antioxidants’ activities, acceptable physicochemical properties and assured its safety. The organoleptic attributes proved the superiority of the spreadable tofu blends with either fruit or vegetables addition compared to control.
INTRODUCTION
Soybean (Glycine max) has been called the "golden miracle bean" and was the world’s foremost provider of protein, used for healthy food and industrial products1.
The amino acid contents of soybean were 4.5% isoleucine, 7.8% leucine, 6.4% lysine, 1.3% methionine, 1.3% cysteine 4.9% phenylalanine, 3.1% tyrosine, 3.9% threonine, 1.3% tryptophan, 4.8% valine, 7.2% arginine, 2.5% histidine, 4.3% alanine, 11.7% aspartic acid, 18.7% glutamic acid, 4.2% glycine, 5.5% proline and 5.1% serine2. Further, it was assured that soybeans are high in quality, protein soybeans contain all the essential amino acids in adequate amounts needed for health and two- three servings of soy provide ~15-20 g protein and 50-75 mg of isoflavones3.
Soybean protein modulated the expression of genes that regulated lipid metabolism and thyroid hormone, promoting weight loss4. This mechanism might attenuate metabolic changes that occur in obesity, which are related to insulin resistance5.
The use of soy as food ingredient has recently grown in food industry as a result of its health benefits, technological and functional properties 6. Soybeans found to be a rich source of phytochemicals and many of those compounds showed important beneficial effects on human and animal health. The important phytochemicals in soybeans for human health were phytoestrogens, mainly isoflavones7.
Tofu used to be made from soybeans, water and a coagulant or curdling agent. It was not only the staple of Asian cuisines, but also became popular in Western cooking for its qualities and nutritive value8.
Tofu contained 88% moisture, 6% protein, ~3% lipids, ~2% carbohydrates and 0.6% ash on dry weight basis. Isoflavones content of tofu was greatly reduced to be 532 mg isoflavones and having no cholesterol or lactose and small quantities of saturated fatty acids9.
Tofu proved to have a high content of calcium that women would need during menopause. It helps to prevent hot flashes and high bone-loss risk related to menopause and during pre-menopausal stage and effective in preventing rheumatoid arthritis10.
Tofu, being a significant source of selenium, could protect from colon cancer and reduce the risk of prostate cancer. Women consuming good amounts of tofu showed sixty percent less likely to have ‘high risk’ breast tissues than those getting fewer amounts or do not eat tofu11.
Using tofu as least expensive substitute of milk cheese with vegetables and fruits containing several beneficial phytochemicals could open new avenues for developing acceptable tofu blends and help in reducing raw material costs. Thus, the present study aimed to determine the effect of mixing tofu with some commodities on the chemical composition, microbiological quality, physicochemical properties and sensory attributes of spreadable tofu products with different flavors to be used as functional foods.
MATERIALS AND METHODS
Soybean seeds (Glycine Max., L., commercial variety) were obtained from Legumes Research Department, Field Crops Research Institute, Agriculture Research Center, Giza, Egypt.
All the added commodities (fruits and vegetables) were purchased from local market at Giza.
Plate count agar, McConky agar, malt agar and tryptone soy agar media were purchased from Difco Co (USA).
Preparation of tofu: The present study was carried out in Dairy Research Institute during the period December, 2015-December, 2017. Processing procedure of tofu is illustrated in Fig. 112,13.
Preparation of spreadable tofu with some commodities: Six blends of spreadable tofu with different flavors were formulated and prepared.
| Fig. 1: | Processing procedure of tofu products from soybeans |
| Table 1: | Formulation of ingredients in different spreadable tofu blends |
C: Control, spreadable tofu without any flavor, T1: Spreadable tofu with Chopped green olives, T2: Spreadable tofu with Mix ground black pepper and chopped green peppers, T3: Spreadable tofu with sugar, T4: Spreadable tofu with guava pulp, T5: Spreadable tofu with peach pulp |
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The raw materials with added commodities and water were added consecutively in Laboratory Processing Kettle (Thermomix TM 31 made in Australia Pty Ltd 2010). The mixture was cooked for 10 min at 85-90°C using indirect steam at pressure 2-2.5 kg cm–2 then was hot filled into wide mouth glass jars and capped directly after filling. The spreadable tofu samples were analyzed at 0, 1, 2 and 3 months of storage in refrigerator (5±2°C). Formulation of the six tofu blends is shown in Table 1.
Chemical analysis: Moisture, total proteins, fat, salt and ash contents were determined as described in Official Methods of Analysis of Association of Official Analytical Chemists (AOAC)14. Carbohydrate content was calculated by subtraction of the sum of moisture, protein, fat and ash contents.
For determination, separation and quantification of phenolic acids and flavonoids compounds, samples were prepared according to Jakopic et al.15. All components were identified and quantified by comparison of peak areas with external standards16.
Radical-scavenging activity by using 2,2-Diphenyl 1-picrylhydrazyl (DPPH) was performed using an ELX800 Microplate Reader (Bio-Tek Instruments, Inc.), according to Abdul-Wahab et al.17.
Total phenolics were estimated based on procedures described by Maurya and Singh18.
Flavonoids determination was performed according to Olajire and Azeez19.
Physicochemical properties: Values of pH were measured using a digital pH meter (HANNA) with combined glass electrode (Electric Instruments Limited).
The oil separation index of spreadable tofu blend was determined according to Thomas20.
Microbiological examinations: Total plate count (TPC) was recorded as colony numbers per gram of sample, yeast and mould count (Chikere and Udochukwu)21, detection of coliform group, Staphylococcus aureus and Listeria monocytogenes as described by Katase and Tsumura22.
Sensory evaluation: Sensory properties of samples were assessed by a panel using hedonic scale where 1-10 represents dislike extremely to like extreme. Sample of spreadable tofu blends were sensory evaluated for appearance (20 points), body and texture (40 points) and flavor (40 points).
Statistical analysis: The obtained data of the chemical components of each treatment and control were statistically analyzed by one-way analysis of variance and organoleptic scores were subjected to two-way of analysis. Least significant differences were estimated under a significance thresholds value of p<0.05. Data were analyzed using SPSS version 20.0 (SPSS Inc., Chicago, IL, USA).
RESULTS
Chemical composition of spreadable tofu products: Data in Table 2 show slight differences among the treatments within the ranges of moisture, protein, fat and ash (55.54-61.39, 15.56-16.93, 18.12-18.8 and 2.67-3.27%, respectively). Insignificant differences were found among both fat and ash contents of the blends. Calculated total carbohydrates ranged from 1.28-6.51%.
Antioxidants activities: Data in Fig. 2 indicate that antioxidants’ activities fluctuated between about 66 and 80% at zero time and after storage up to 3 months, which were close.
| Fig. 2: | Antioxidants’ activities of different spreadable tofu products |
C: Control, spreadable tofu without any flavor, T1: Spreadable tofu with Chopped green olives, T2: Spreadable tofu with Mix ground black pepper and chopped green peppers, T3: Spreadable tofu with sugar, T4: Spreadable tofu with guava pulp, T5: Spreadable tofu with peach pulp |
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| Table 2: | Chemical composition of different spreadable tofu blends |
C: Control, spreadable tofu without any flavor, T1: Spreadable tofu with chopped green olives, T2: Spreadable tofu with mix ground black pepper and chopped green peppers, T3: Spreadable tofu with sugar, T4: Spreadable tofu with guava pulp, T5: Spreadable tofu with peach pulp |
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| Table 3: | Isoflavones components of spreadable tofu blends |
C: Control, spreadable tofu without any flavor, T1: Spreadable tofu with chopped green olives, T2: Spreadable tofu with mix ground black pepper and chopped green peppers, T3: Spreadable tofu with sugar, T4: Spreadable tofu with guava pulp, T5: Spreadable tofu with peach pulp |
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The antioxidants’ activities of all the blends were higher than that of control. The antiradical activity was evaluated from the plot of percentage DPPH showed increases in the treatments compared to control before storage and after storage up to 3 months, all treatments demonstrated slight decreases throughout storage. The highest activities were observed for T2 and T4, followed by T5 and then T2 blends with fruits, vegetables and spices. In contrast, the lowest values was recorded for T3 and control.
Isoflavones: The concentrations of isoflavones shown in Table 3 demonstrate that total isoflavones of spreadable tofu ranged from 2181-3259 μg g–1. All treatments were high in genistein, daidzein and low in isoformntine and biochainine. The control sample demonstrated a higher concentration of isoflavones compared to other treatments.
Phenolic compounds: Twenty-one phenolic compounds of tofu spreadable blends were measured (Table 4). The phenolic compounds found in the different spreadable tofu blends included pyrogallol, gallic, 4-Aminobenzoic, protocatechuic, catechin, catechol, chlorogenic, epicatechin, p-OH-benzoic, caffeine, vanillic, caffeic, p-coumaric, ferulic, iso-ferulic, oleuropein, benzoic, ellagic, coumarin, salicylic and cinnamic. The highest values of phenolic compounds were in order as follows: Ellagic, benzoic, catechin, pyrogallol and ferulic.
| Fig. 3: | The pH value of spreadable tofu products(%) throughout storage for 3 months |
C: Control, spreadable tofu without any flavor, T1: Spreadable tofu with Chopped green olives, T2: Spreadable tofu with Mix ground black pepper and chopped green peppers, T3: Spreadable tofu with sugar, T4: Spreadable tofu with guava pulp, T5: Spreadable tofu with peach pulp |
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| Table 4: | Phenolic compounds in spreadable tofu blends |
C: Control spreadable tofu without any flavor, T1: Spreadable tofu with chopped green olives, T2: Spreadable tofu with mix ground black pepper and chopped green peppers, T3: Spreadable tofu with sugar, T4: Spreadable tofu with guava pulp, T5: Spreadable tofu with peach pulp |
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Other phenolic detected compounds had very little amounts in soybean seed and tofu. Oleuropein was only found in T1.
Flavonoid compounds: Results in Table 5 show that in tofu blends, flavonoid compounds (naringin, hesperidin, rutin, rosmarinic, quercetin, naringenin, hesperetin, kaempferol and apigenin) were present. The highest values were scored for naringin (378-887), hesperidin (304-812), quercetrin (128-457), naringenin (118-174) and hesperetin (94-138) μg g–1, while the lowest phenolic compound was kaempferol (4-32 μg g–1).
Physicochemical properties of products
pH value: The data in Fig. 2 indicate that the pH values of fresh blends ranged from 5.88-6.82 and at the end of the storage period were 5.70-6.80. Generally, pH values of all treatment were higher than that of control before and after 3 months of storage. Results also indicated that adding the ratio of fruit additives in the blends, decreased pH value of the treatments.
Oil separation: Data in Fig. 3 indicate that spreadable tofu with pepper and guava had the lowest fat separation index compared to the other samples.
| Fig. 4: | Changes in oil separation of spreadable tofu products (%) throughout storage for 3 months |
C: Control, spreadable tofu without any flavor, T1: Spreadable tofu with chopped green olives, T2: Spreadable tofu with mix ground black pepper and chopped green peppers, T3: Spreadable tofu with sugar, T4: Spreadable tofu with guava pulp, T5: Spreadable tofu with peach pulp |
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| Table 5: | Flavonoid compounds in spreadable tofu blends |
C: Control spreadable tofu without any flavor, T1: Spreadable tofu with chopped green olives, T2: Spreadable tofu with mix ground black pepper and chopped green peppers, T3: Spreadable tofu with sugar, T4: Spreadable tofu with guava pulp, T5: Spreadable tofu with peach pulp |
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| Table 6: | Microbiological properties of spreadable tofu products ( log CFU g–1) |
ND: Not detected, C: Control spreadable tofu without any flavor, T1: Spreadable tofu with chopped green olives, T2: Spreadable tofu with mix ground black pepper and chopped green peppers, T3: Spreadable tofu with sugar, T4: Spreadable tofu with guava pulp, T5: Spreadable tofu with peach pulp, TBC: Total bacteria count |
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The fat separation was increased with extending the storage period.
Microbiological properties: Obtained data in Table 6 showed that yeasts and molds, coliform groups, Listeria and Staphylococci were not detected in all the samples throughout the storage period. Spreadable tofu product after 3 months of storage (C, T1, T2, T3, T4 and T5) had 3.34, 5.13, 2.78, 2.69, 3.3 and 3.04 log CFU g–1, respectively.
Sensory evaluation: Data in Table 7 show that the sensory test of spreadable tofu blends proved the superiority of green olive sample compared to pepper sample for flavor and total acceptability. Meanwhile, guava sample showed significantly higher acceptability scores than peach (p>0.05). However, control spreadable tofu was less significantly acceptable than all the other blends (p>0.05). All organoleptic properties of the spreadable tofu blends except the appearance of T4 were significantly decreased (p>0.05) after 3 months storage due to the effect of storage.
| Table 7: | Sensory evaluation of spreadable tofu products during storage (3 months) |
Means with unlike superscript letters were significantly different (α = 0.05), C: Control spreadable tofu without any flavor, T1: Spreadable tofu with 5% chopped green olives, T2: Spreadable tofu with 2.7% mix ground black pepper and chopped green peppers, T3: Spreadable tofu with 2% sugar, T4: Spreadable tofu with 20%guava pulp, T5: Spreadable tofu with 15% peach, 0: Fresh, 1: 1 month, 2: 2 month, 3: 3 months |
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DISCUSSION
The moisture contents of the prepared tofu blends were in harmony with those of tofu creamy cheese23. A food products containing 1-25% fat was defined as low fat, the prepared spreadable tofu blends contained about 18% could be categorized as low-fat products24. Total carbohydrates were in the same line with Nazim et al.9.
Regarding the antioxidant activity, the increase of the Free Radical Scavenging Activities (FRSA) for different treatments resulted from the added materials. These results are in harmony with those of Huang et al.25. Tofu prepared with garcinia extract showed high FRSA (82.1%), due to the polyphenolic compounds present in fruit extracts26.
The control sample showing a higher concentration of isoflavones compared to other treatments might be due to the higher percentage of tofu in control. The major compounds in all the prepared blends reflected the compounds in tofu that were close to those of Chung et al.27. The high contents of genistein, daidzein and the low contents of isoformntine, biochainine confirmed those of Chung et al.27.
The slight differences of isoflavones composition compared with other studies on soybean products could be ascribed to environmental and botanic characteristics and process technologies of analyzed samples28.
Positive effects of isoflavones on heart health, bone health and post-menopausal symptoms effects are highly attractive to the functional foods market29,30.
The presence of oleuropein in T1 only attributed to the addition of olives, a distinctive compound in olive fruits and not appearing in the rest of the other treatments, confirmed by Omar31, who noted antioxidant, anti-inflammatory, anti-atherogenic, anti-cancer, antimicrobial and antiviral of oleuropein. Bulotta et al.32 concluded that oleuropein showed cardioprotective properties against acute adriamycin cardiotoxicity and exhibited anti-ischemic and hypolipidemic activities. The study of Barbaro et al.33, proved that adding oleuropein increased the ability of LDL to resist oxidation and at the same time reduced the plasma levels of total, free and esterified cholesterol.
Prasain34, Otaki et al.,35 and Thilakarathna and Rupasinghe36 suggested that flavonoids showed a promise as useful adjuvants to prevent, delay and/or ameliorate several chronic diseases in aging humans including cancer, cardiovascular disease and cognitive impairments. Perhaps the greatest future impact of botanicals in age-related disease will be related to reducing the impact of the major contributors to the metabolic syndrome, since each of them is very closely linked to diet (e.g., excess fat and carbohydrate ingestion).
Physicochemical properties of products showing high pH value increasing of all treatment with tofu could be due to the high pH value of tofu used in the formula (6.00)37. The decrease of pH blends with fruits might be due to the limited growth and activity of fruit microflora and changes occurred in emulsifying salt form37.
The oil index value depended on the state of fat and protein in resultant spreadable tofu emulsion, affected by type and amount of raw materials in the base formula, pH value, cooking time and temperature. Storage of samples increased the free oil in the product. Oiling was increased as the concentration of soy cheese increased38,39, these findings were in the same line with those of previous studies of Azam40 and Hussein et al.41.
The fat separation was gradually increased with extending the storage period, which could be attributed to the nature of tofu protein that might affect the emulsification degree of the product. The oil index value depended on the state of fat and protein in resultant spreadable tofu emulsion, which could be affected by type and amount of raw materials in the base formula, pH value, cooking time and temperature. Storage of samples increased the free oil in the product confirmed by other researchers41,42.
The microbiological properties confirmed that yeasts and moulds and coliform groups were not detected in tofu stored at refrigerator (4°C) even after 15 days of storage43,44. Heat treatment ultimately reduced the occurrence of the potentially harmful organisms and increased the shelf life of soy products45.
As sensory evaluation, an important indicator of consumer preferences, all organoleptic properties of the spreadable tofu blends except the appearance of T4 were significantly decreased (p>0.05) after 3 months of storage due to the effect of storage period. The sensory panel test confirmed the similar trend noticed by El-Boraey45 about beany taste and flavor that undoubtedly were the very important constituents to like or dislike a product as mentioned by Murugkar13. The presence of beany flavor and off smell of soy products appeared to be one of the biggest hindrances in its promotion as a healthy food. Food additives is known to reduce undesirable flavors to a minimum and maximize total acceptability for tofu, good color characteristics and was found highly acceptable by panelists13.
CONCLUSION AND FUTURE RECOMMENDATIONS
The present study confirmed that the formulated tofu blends exhibited high antioxidants’ activities, acceptable physicochemical properties and assured its safety. The organoleptic attributes proved the superiority of the spreadable tofu blends with either fruit or vegetables addition compared to control.
Consumers might be not aware of spreadable tofu blends and thus, introducing such products through marketing would be recommended. Further studies would be needed to use such blends in some popular foods such as bakery products as filling materials.
SIGNIFICANT STATEMENT
In the present study, new six tofu blends were formulated and prepared. The first blend contained only tofu without addition as control. In the five other blends vegetables and fruits were added to tofu to improve the taste, odor and its antioxidants activities. These blends could be used for its health benefits, technological and functional properties. The study would help researchers to use and incorporate such blends in some products to be used as inexpensive supplementary meals. Feeding several groups of populations would benefit health promotion of the whole society. This study confirmed that the formulated spreadable tofu blends exhibited high antioxidants’ activities, acceptable physicochemical and organoleptic properties and assured its safety. The spreadable tofu blends proved the superiority of spreadable tofu blends compared to control.