1. Please check and comment entries here.
Table of Contents

    Topic review

    Grape Pomace for Tofu Production

    View times: 9
    Submitted by: Giuseppe Zeppa

    Definition

    Tofu, soybean curd, or bean curd is one of the most important soya products and is produced by the addition of coagulants (acids, salts or enzymes) to soymilk. It is widely consumed in Asia and has been growing in popularity worldwide because of its high nutritional value, good texture, and unique flavour. It has high contents of highly digestible proteins, dietary fibre, soy saponins, and isoflavones that can prevent the progression of arteriosclerosis by reducing plasma lipids. Furthermore, tofu is cholesterol-free and has a lower amount of saturated fat than animal sources of protein, such as meat or milk.  Mixing different types of coagulants can potentially overcome the disadvantages of a single coagulant and improve the quality of tofu although research efforts have also explored new coagulants to replace traditional ones. Grape pomace (GP) can be used as a coagulating agent for tofu production. The GP, composed of a mix of grape seeds and skins, corresponds to approximately 62% of the total waste generated during the winemaking process. GPs are partially distilled for ethanol extraction, although most of this by-product is discarded, with several environmental and economic effects. Nevertheless, GPs are rich sources of high-value compounds, such as acids (tartaric, malic, and citric), fibres, polyphenols, and salts, and have been widely suggested as ingredients in pasta, puree, biscuits, yoghurt, cereal bars, pancakes, and cheese. Moreover, distilled GPs are rich sources of high-value compounds, although in contrast to fresh GPs, no applications have been suggested for distilled GPs; therefore, the problem of the disposal of fresh and distilled GPs still needs to be solved, and their use as ingredients in foods facilitates green production and the minimisation of by-product treatment costs, creating new sources of income for grape producers and increasing consumer interest in healthier foods. Furthermore, the addition of grape by-products to foods may represent a novel strategy to produce functional foods with high contents of polyphenols and high antioxidant activity. Since high concentrations of acids and salts are present in GPs,  these by-products could act as coagulants for soy proteins. The possibility of their use in tofu production is very good in regard to reducing winemaking waste and obtaining new and innovative functional foods with high contents of polyphenols that are completely produced from vegetables.

    1. Overview

    Tofu, one of the most important products made from soymilk, is obtained through a coagulation process performed with various coagulants (acids, salts and, enzymes). Innovative tofu samples were produced using the grape pomace (GP) powders of different varieties (Barbera, Chardonnay, Moscato, and Pinot Noir) with different origins (fermented and distilled) at two concentration levels (2.5% and 5% w/v) as coagulants, and comparisons with traditional tofu were made. Physicochemical characteristics, phenolic contents, radical scavenging activity levels, textural properties, and consumer acceptability were evaluated. The moisture, protein content, and pH levels of GP tofu samples were slightly lower than those of traditional tofu. Regarding textural parameters, except for hardness, all other parameters were significantly lower in GP tofu samples, with differences due to GP concentration. The colours of GP tofu varied from amber-yellow to violet according to the GP origin. The blue-violet colours were observed predominantly in tofu samples obtained with Barbera and Pinot Noir GPs, while the other GP tofu samples showed amber-yellow colours. The concentrations of polyphenols were 2–10 times higher than in traditional tofu, while the radical scavenging activity levels were 9–80 times higher. The GP tofu samples were favoured by consumers, with small differences among the GP varieties.

    2. Tofu

    Tofu, soybean curd, or bean curd is one of the most important soya products and is produced by the addition of coagulants to soymilk. It is widely consumed in Asia and has been growing in popularity worldwide because of its high nutritional value, good texture, and unique flavour [1]. It has high contents of highly digestible proteins, dietary fibre, soy saponins, and isoflavones that can prevent the progression of arteriosclerosis by reducing plasma lipids [2][3][4]. Furthermore, tofu is cholesterol-free and has a lower amount of saturated fat than animal sources of protein, such as meat or milk [5].
    There are two major steps in tofu production: heating soymilk and coagulation of soymilk to obtain a curd [1][6].
    Heating soymilk causes denaturation of soy protein and exposure of the inner hydrophobic groups [7]. Electrostatic repulsion extensively opposes protein–protein interactions, preventing gel formation, while the balance of attraction and repulsion forces in protein molecules determines the stability of soymilk [7]. The heating of soymilk is also an essential step in the denaturation of antinutritional compounds [8]. Coagulation is then achieved by the addition of a coagulant, while hydrophobic interactions of the denatured protein lead to the aggregation of protein molecules, thereby forming curd [9][10].
    The physical, textural, and sensory properties of the obtained tofu are affected by multiple factors that can be classified as intrinsic (i.e., composition of soya seeds) and extrinsic (i.e., processing conditions and packaging) factors [11][12][13]. The most critical step in the processing is the coagulation phase, which involves the selection of a coagulant [6][14][15][16]. At present, common coagulants are divided into three main groups: acids, salts, and enzymes [6][13]. The driving forces behind the acid gelation of soy proteins are isoelectric precipitation, including salt bridging, and direct interactions, such as hydrogen bonding and van der Waals forces [8][16]. With salts, a three-dimensional network structure is formed by forming salt bridges to cross-connect protein molecules [6]. In particular, phytic acids interact with Ca2+ to form non-ionising products that allow interactions between Ca2+ and proteins. Then, Ca2+ interacts with non-particulate proteins to form new protein particles, which are associated with each other to develop the gel network [17]. Enzyme coagulants such as transglutaminase can assemble proteins with the help of isopeptide bonds that are formed from the amine group in the glutamine residue and the ξ-amino group in the lysine residue [11]. Fermented soy whey, glucose-delta-lactone (GDL), and citric acid are commonly used acidic coagulants [6][14][16][18], while calcium sulphate, calcium chloride, calcium acetate, calcium lactate, and magnesium chloride are commonly used salt coagulants [5][19]. Magnesium chloride allows the taste of soybean to be retained and creates a more natural flavour for tofu; however, it is a quick-acting coagulant with a lower yield, forming a harder and non-uniform tofu [5].
    Many studies have been devoted to evaluating the effects of these different coagulants on tofu quality. Shi et al. [6] studied the effects of four different coagulants (magnesium chloride, calcium sulphate, GDL, and fermented soybean whey) on the gelation behaviour of tofu, and their results showed a significant effect on the physicochemical properties, textural characteristics, and volatile flavour profile. In particular, the calcium sulphate tofu had the best overall acceptance in terms of sensory evaluation, while magnesium chloride tofu displayed the best gumminess, resilience, and mouthfeel.
    Zhao et al. [18] evaluated the effects of different salts (potassium chloride, calcium chloride, and calcium sulphate) on the gelation of citric-acid-induced tofu and showed that this addition improved the mechanical properties of the product. In fact, the balance between forces that are suitable for gel structure leads to an increase in the storage modulus.
    Cao et al. [16] studied the effects of different organic acids (citric, malic, and tartaric) on tofu quality, highlighting that tofu prepared with organic acids is comparable to that obtained with GDL, although the product prepared with tartaric acid had comparatively poorer physical properties and less robust chemical interactions. Acidification was also obtained with commercial lactic cultures, which in comparison with GDL showed a significantly earlier gel point but a similar final gel structure [8].
    The structure and formation mechanism of tofu induced by different types of coagulants (GDL, calcium sulphate (CS), and microbial transglutaminase (MTGase)) were studied by Wang [20]. MTGase produced gels with an intermediate structure between CS and GDL but with the best uniformity. Similar work was performed by Rui et al. [21] who investigated the effects of different coagulants (GDL, magnesium chloride (MC), and MTGase) on the degradation of soybean proteins; their results showed that the MTGase tofu had the lowest protein digestibility when compared to the gels prepared with MC and GDL. Ezeama and Dobson [22] used Epson salt, lime, and tamarind to make tofu, showing that the fresh product obtained with Epson salt was well received by consumers because of its high calcium, magnesium, and protein contents.
    Mixing different types of coagulants can potentially overcome the disadvantages of a single coagulant and improve the quality of tofu [1][5][13][18][20][23], although research efforts have also explored new coagulants to replace traditional ones. Crab shell powder [24], roselle water extract [25], trimagnesium citrate [26], papain [27], and commercial rennet have been used [28]. As highlighted by Zheng et al. [13], the use of a new coagulant requires not only the evaluation of its impacts on the compositional, textural, and sensory characteristics of tofu, but also its feasibility according to local availability and production costs; therefore, the purpose of this study was to evaluate the possibility of using grape pomace (GP) as a coagulating agent for tofu production. The GP, composed of a mix of grape seeds and skins, corresponds to approximately 62% of the total waste generated during the winemaking process [29]. GPs are partially distilled for ethanol extraction, although most of this by-product is discarded, with several environmental and economic effects [29]. Nevertheless, GPs are rich sources of high-value compounds, such as acids (tartaric, malic, and citric), fibres, polyphenols, and salts, and have been widely suggested as ingredients in pasta, puree, biscuits, yoghurt, cereal bars, pancakes, and cheese [29]. Moreover, distilled GPs are rich sources of high-value compounds, although in contrast to fresh GPs, no applications have been suggested for distilled GPs; therefore, the problem of the disposal of fresh and distilled GPs still needs to be solved, and their use as ingredients in foods facilitates green production and the minimisation of by-product treatment costs, creating new sources of income for grape producers and increasing consumer interest in healthier foods. Furthermore, the addition of grape by-products to foods may represent a novel strategy to produce functional foods with high contents of polyphenols and high antioxidant activity. Since high concentrations of acids and salts are present in GPs [29], these by-products could act as coagulants for soy proteins. The possibility of their use in tofu production is very good in regard to reducing winemaking waste and obtaining new and innovative functional foods with high contents of polyphenols that are completely produced from vegetables.

    3. Conclusions

    Tofu samples coagulated with Moscato and Chardonnay pomaces were very similar, with a “woody” colour and semi-solid texture. These tofu samples were characterised by a high quantity of sugars, similar to those obtained with fresh pomace. The tofu produced with the pomace of Pinot Noir was found to be the most consistent and dry. Finally, the tofu produced with Barbera pomace created some difficulties during production due to the formation of very fine curds, and consequently its soft and almost spreadable consistency. These two tofu samples were characterised by higher total polyphenol contents and radical scavenging activity levels. All of the obtained tofu samples were naturally coloured, and this characteristic is important from a commercial point of view. Generally, there were no differences between tofu samples according to the distillation process, while there were significant differences due to grape variety.
    From the point of view of sensory characteristics, the tofu made using Barbera pomace had the greatest acceptability, although these results need to be confirmed by new and specific tests carried out with a greater number of consumers.
    The tofu obtained with pomace is achievable on a technological level, as pomace naturally contains salts and acids; furthermore, since GPs are rich in polyphenolic compounds, they give tofu a functional value.
    An ideal coagulant should be economical (i.e., affordable in most developing countries and especially in the least developed countries), convenient, have an efficient extraction rate, have possible use as an antioxidant, and have other functional properties, in addition to being highly nutritional and environmentally friendly. GPs have all of these characteristics, and the reuse of such pomaces in a new production process is valuable in order not to waste them. Their utilisation can also decrease the costs of winemaking.

    The entry is from 10.3390/foods10081857

    References

    1. Guo, Y.; Hu, H.; Wang, Q.; Liu, H. A novel process for peanut tofu gel: Its texture, microstructure and protein behavioral changes affected by processing conditions. LWT 2018, 96, 140–146.
    2. Lee, K.Y.; Rahman, M.S.; Kim, A.N.; Gul, K.; Kang, S.W.; Chun, J.; Kerr, W.L.; Choi, S.G. Quality characteristics and storage stability of low-fat tofu prepared with defatted soy flours treated by supercritical-CO2 and hexane. LWT 2019, 100, 237–243.
    3. Kim, D.H.; Yang, W.T.; Cho, K.M.; Lee, J.H. Comparative analysis of isoflavone aglycones using microwave-assisted acid hydrolysis from soybean organs at different growth times and screening for their digestive enzyme inhibition and antioxidant properties. Food Chem. 2020, 305, 125462.
    4. Wang, E.; Li, Y.; Maguy, B.L.; Lou, Z.; Wang, H.; Zhao, W.; Chen, X. Separation and enrichment of phenolics improved the antibiofilm and antibacterial activity of the fractions from Citrus medica L. var. sarcodactylis in vitro and in tofu. Food Chem. 2019, 294, 533–538.
    5. Li, M.; Chen, F.; Yang, B.; Lai, S.; Yang, H.; Liu, K.; Bu, G.; Fu, C.; Deng, Y. Preparation of organic tofu using organic compatible magnesium chloride incorporated with polysaccharide coagulants. Food Chem. 2015, 167, 168–174.
    6. Shi, Y.G.; Yang, Y.; Piekoszewski, W.; Zeng, J.H.; Guan, H.N.; Wang, B.; Liu, L.; Zhu, X.Q.; Chen, F.L.; Zhang, N. Influence of four different coagulants on the physicochemical properties, textural characteristics and flavour of tofu. Int. J. Food Sci. Technol. 2020, 55, 1218–1229.
    7. Totosaus, A.; Montejano, J.G.; Salazar, J.A.; Guerrero, I. A review of physical and chemical protein-gel induction. Int. J. Food Sci. Technol. 2002, 37, 589–601.
    8. Grygorczyk, A.; Corredig, M. Acid induced gelation of soymilk, comparison between gels prepared with lactic acid bacteria and glucono-δ-lactone. Food Chem. 2013, 141, 1716–1721.
    9. Kohyama, K.; Sano, Y.; Doi, E. Rheological Characteristics and Gelation Mechanism of Tofu (Soybean Curd). J. Agric. Food Chem. 1995, 43, 1808–1812.
    10. McClements, D.J.; Keogh, M.K. Physical properties of cold-setting gels formed from heat-denatured whey protein isolate. J. Sci. Food Agric. 1995, 69, 7–14.
    11. Zhang, Q.; Wang, C.; Li, B.; Li, L.; Lin, D.; Chen, H.; Liu, Y.; Li, S.; Qin, W.; Liu, J.; et al. Research progress in tofu processing: From raw materials to processing conditions. Crit. Rev. Food Sci. Nutr. 2018, 58, 1448–1467.
    12. Wang, R.; Jin, X.; Su, S.; Lu, Y.; Guo, S. Soymilk gelation: The determinant roles of incubation time and gelation rate. Food Hydrocoll. 2019, 97, 105230.
    13. Zheng, L.; Regenstein, J.M.; Teng, F.; Li, Y. Tofu products: A review of their raw materials, processing conditions, and packaging. Compr. Rev. Food Sci. Food Saf. 2020, 19, 3683–3714.
    14. Li Tay, S.; Yao Tan, H.; Perera, C. The Coagulating Effects of Cations and Anions on Soy Protein. Int. J. Food Prop. 2006, 9, 317–322.
    15. Bi, C.H.; Li, D.; Wang, L.J.; Adhikari, B. Viscoelastic properties and fractal analysis of acid-induced SPI gels at different ionic strength. Carbohydr. Polym. 2013, 92, 98–105.
    16. Cao, F.H.; Li, X.J.; Luo, S.Z.; Mu, D.D.; Zhong, X.Y.; Jiang, S.T.; Zheng, Z.; Zhao, Y.Y. Effects of organic acid coagulants on the physical properties of and chemical interactions in tofu. LWT Food Sci. Technol. 2017, 85, 58–65.
    17. Shun-Tang, G.; Ono, T.; Mikami, M. Incorporation of soy milk lipid into protein coagulum by addition of calcium chloride. J. Agric. Food Chem. 1999, 47, 901–905.
    18. Zhao, Y.Y.; Cao, F.H.; Li, X.J.; Mu, D.D.; Zhong, X.Y.; Jiang, S.T.; Zheng, Z.; Luo, S.Z. Effects of different salts on the gelation behaviour and mechanical properties of citric acid-induced tofu. Int. J. Food Sci. Technol. 2020, 55, 785–794.
    19. Zuo, F.; Chen, Z.; Shi, X.; Wang, R.; Guo, S. Yield and textural properties of tofu as affected by soymilk coagulation prepared by a high-temperature pressure cooking process. Food Chem. 2016, 213, 561–566.
    20. Wang, X.; Luo, K.; Liu, S.; Zeng, M.; Adhikari, B.; He, Z.; Chen, J. Textural and Rheological Properties of Soy Protein Isolate Tofu-Type Emulsion Gels: Influence of Soybean Variety and Coagulant Type. Food Biophys. 2018, 13, 324–332.
    21. Rui, X.; Fu, Y.; Zhang, Q.; Li, W.; Zare, F.; Chen, X.; Jiang, M.; Dong, M. A comparison study of bioaccessibility of soy protein gel induced by magnesiumchloride, glucono-δ-lactone and microbial transglutaminase. LWT Food Sci. Technol. 2016, 71, 234–242.
    22. Ezeama, C.F.; Dobson, G.N. Effect of coagulants on the physicochemical properties of fresh tofu. Afr. J. Food Sci. 2019, 13, 287–296.
    23. Zhu, Q.; Wu, F.; Saito, M.; Tatsumi, E.; Yin, L. Effect of magnesium salt concentration in water-in-oil emulsions on the physical properties and microstructure of tofu. Food Chem. 2016, 2016, 197–204.
    24. Jun, J.Y.; Jung, M.J.; Jeong, I.H.; Kim, G.W.; Sim, J.M.; Nam, S.Y.; Kim, B.M. Effects of crab shell extract as a coagulant on the textural and sensorial properties of tofu (soybean curd). Food Sci. Nutr. 2019, 7, 547–553.
    25. Fasoyiro, S.B. Physical, Chemical and Sensory Qualities of Roselle Water Extract-coagulated Tofu Compared with Tofu from Two Natural Coagulants. Niger. Food J. 2014, 32, 97–102.
    26. Joo, K.H.; Cavender, G.A. Investigation of tofu products coagulated with trimagnesium citrate as a novel alternative to nigari and gypsum: Comparison of physical properties and consumer preference. LWT 2020, 118, 108819.
    27. Rizkaprilisa, W.; Setiadi, S. Comparative Study of CaSO4 and Papain Enzyme as Coagulants in the Tofu Production. Indones. Food Nutr. Prog. 2018, 15, 79–84.
    28. Stanojevic, S.P.; Barać, M.B.; Pešić, M.B.; Vucelic-Radovic, B.V. Protein composition and textural properties of inulin-enriched tofu produced by hydrothermal process. LWT 2020, 126, 109309.
    29. Lavelli, V.; Torri, L.; Zeppa, G.; Fiori, L.; Spigno, G. Recovery of Winemaking By-Products. Ital. J. Food Sci. 2016, 28, 542–564.
    More