Prebiotic production from Agrofood Wastes: An Opportunity to develop high value compounds and generate employment

Fig 1: Food processing byproducts. Credit: Manoj Kumar Tripathi

Increase in agricultural production and their processing simultaneously generating a higher amount of by-products and wastes. Fruit and vegetables byproducts such as bagasse, peels, trimmings, stems, shells, bran, and seeds account for more than 50% of fresh fruit, and sometimes their nutritional or functional content are higher than the final product (Fig 1). These nutritionally rich agricultural and food processing by?products can be used as main source of functional or nutraceutical ingredients. Byproducts and waste generation are having an impact on environmental, economic, and social sectors, as they  contribute to Green House Gas (GHG) emissions.

Many or almost all of these products are always discarded, and they can be utilized for making prebiotic rich foods. Potential resources of by?products from food processing for production of prebiotics are generally derived from various food industries and some are from agricultural wastes or by?products. In the prebiotic food market, apart from prebiotic  from various fruits and vegetables, resistant starch can also be found in a wide variety of agricultural products rich in starch, such as legumes, grains, roots and also derived from food ingredient added. Development of some secondary food products and supplements applying food wastes or by-products from different agro-industries is a great alternative for efficient utilization and management of these agro wastes, thus generating income and employment also.

Prebiotics are generally defined as non-digestible polysaccharides and oligosaccharides (NDO), which promote the growth of beneficial lactic acid bacteria in the colon and exert antagonism to Salmonella sp. or Escherichia coli, limiting their proliferation. There exists an array of prebiotics with different chemical properties which are obtained from various origin. In addition to supplementation of minerals, vitamins and antioxidants in foods, it would be of interest to consider the possibility of adding prebiotics to induce a faster production of lactic acid bacteria in the food product as well as in the gut. Prebiotics such as dietary fibers with high viscoelasticity imparts better sensory perception, lower digestible starch and higher resistant starch contents, thereby lowering down the in vitro expected glycemic index. Food products made with a combination of different prebiotics and probiotics improve health benefits. The diversification of food products and the growing interest in healthy life requires innovations from food industry. Different dehydrated prebiotic fibers viz. oat bran, b-glucan and green banana flour have been found to provid substratum for adherence and trehalose acted as a cell protectant prolonging the viability of L. casei. In the sensory evaluation, the prebiotic oat bran added to a dairy fruit beverage has been well accepted by consumers.

Prebiotics have a positive influence on the gut-associated lymphoid tissues (GALT). Many prebiotics are currently used in different therapeutic nutritional preparations for optimum gut function which favour the proliferation of normal bacterial flora and inhibit the growth of pathogenic organisms. The consumption of prebiotics can modulate immune factors in GALT, secondary lymphoid tissues and peripheral circulation (Bodera 2008). Probiotic and prebiotic administration influence the intestinal bacterial community and quickening the growth of commensal bacteria. In case of prebiotic supplemented formula it was found to increase stool colony counts of bifidobacteria and lactobacilli without harmfully affecting weight gain (Srinivasjois et al. 2009).

Tofu whey, a by-product obtained during tofu manufacturing which is normally discarded, contains non-digestable oligosaccharides (NDOs). Fermentation of NDOs in the caecum leads to increase in mineral absorption, mainly calcium and magnesium. In view of its possible health-promoting properties, soybean whey may be used as a valuable ingredient in functional foods. Prebiotic oligosaccharides prepared from soy sauce lees (SSLO) have growth promoting effect on some bacteria as L. bulgaricus and S. thermophilus (Yang et al. 2011a). Galacto-oligosaccharides are found in soybeans and other kinds of pulses, whereas raffinose is also found in sugar beet. For industrial production they are extracted from soybean whey, a byproduct from the production of soy protein, and concentrated to oligosaccharide syrup. These α-galacto-oligosaccharides include raffinose, stachyose and verbascose and consist of galactosyl residues linked α-1,6 to the glucose moiety of sucrose. Since α-galactosidase activity is not present among human digestive enzymes, the oligosaccharides can reach the colon intact. Nagura et al (1999) showed that with 5 g/d of raffinose, defecation pattern improves in healthy human volunteers. Their other physiological effects appear to be similar to the other galacto-oligosaccharides; they are bifidogenic and hence other effects can be expected from this change in colon microbiota. Zheng et al. (2012) reported that soybean oligosaccharides have an effect on components of the immune system.

Prebiotic oligosaccharides are also developed from Bengal gram husk and wheat bran using enzymatic action. Prebiotic FOS can also be produced from carrot by-products after the osmotic dehydration. The solid wastes accumulated in malting industries viz. barley husks, spent grains and grain fragments, when processed by hydrothermal techniques, the liquor contained xylo-oligosaccharides. The superior oligosaccharides on fermentation generated succinate, lactate, formate, acetate, propionate and butyrate, which were found to have prebiotic potential. Wang et al. (2010) studied that mung bean may enhance the growth of L. paracasei. Some reports have also indicated about prebiotic potential of pectic oligosaccharide-rich refined product from apple pomace, processed by simultaneous saccharification and solid-state fermentation.

The development of viable solutions for managing the byproducts and food waste is one of the main challenges of our country. With the nutritional problems facing by the society today, the use of food waste for human food should be a priority. Wastes and byproducts produced in developing countries have a great nutritional and functional value to develop value added and healthy food ingredients in food formulation, and may acts as a powerful tool in minimizing hunger. In addition, the added value created by the divergence of the creative chains can create job opportunities for the citizens making an extra social benefit.

References:

Bodera P (2008) Influence of prebiotics on the human immune system (GALT). Recent Pat Inflamm Allergy Drug Discov 2:19–153

Srinivasjois R, Rao S, Patole S (2009) Prebiotic supplementation of formula in preterm neonates: a systematic review and metaanalysis of randomized controlled trials. Clin Nutr 28:237–242

Yang B, Prasad KN, Xie H, Lin S, Jiang Y (2011a) Structural characteristics of oligosaccharides from soy sauce lees and their potential prebiotic effect on lactic acid bacteria. Food Chem 126:590–594

Zheng, R., Yang, L., Zhou, X.-L., Zhu, C., Shu, X.-G., Wu, X., et al. (2012). Effect of soybean oligosaccharides on immunity and TLR2-NF-κB signal pathway response for weanling pigs. Journal of Food, Agriculture & Environment, 10, 273–279.

 

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