Abstract
In this study, the effect of roasting temperatures (110, 120 and 130oC) and times (20, 40, 60, 80, 100 and 120 min) respectively on soybean protein quality test parameters was investigated. Results have revealed that urease activity decreased gradually with increasing time at 110C, suggesting that the test could be a suitable indicator for both under processing and over processing as opposed to 120 and 130C where there was a sudden drop in urease activity. Results further showed that at 110C, protein solubility in potassium hydroxide remained high with increasing time while at 120C, protein solubility decreased inconsistently. On the other hand, protein solubility at 130C decreased steadily suggesting that the test could be a suitable indicator for both under processing and over processing. It was further observed that at all roasting temperatures, protein dispersibility index decreased gradually with the highest and lowest decreases observed at 130C and 110C respectively. Results further showed that at 130C, protein digestibility and protein dispersibility index tests could yield results that were comparable with urease activity and protein solubility tests unlike at 110 and 120C. The findings have demonstrated that roasting temperatures and times significantly affected the test parameters used in determining the adequacy of soybean processing. These findings justify the need to carefully consider roasting temperatures for potential applications of processed soybeans in animal feeds processing as well as product development for human consumption.
Highlights
Soy, a popular legume is widely consumed in many parts of the world including Asia, America, Europe and Africa
It has been well documented that soy contains trypsin inhibitor which in addition to its detrimental effects on proteolytic action (Bora, 2014; Jiang et al, 2013; Newkirk, 2010) and lowering of protein quality (Momonoki et al, 2002) it dramatically increases the size of the pancreas and amount of trypsinogen production (Rocha et al, 2014)
It is generally well recognized that various techniques such as heat treatment, soaking, germination, fermentation, irradiation, fortification and blending have been previously used in soy processing to improve the bioavailability of essential nutrients as well as improving the acceptability of soy products (Agrahar-Murugkar and Jha, 2010; Anderson, 1992; Bajpai et al, 2005; Žilić et al, 2010; Sowonola et al, 2005)
Summary
A popular legume is widely consumed in many parts of the world including Asia, America, Europe and Africa. Because it is highly nutritive in various essential nutrients, it is used as a raw material in development of different food products such as tofu, soymilk, tempeh, soy yoghurt, miso, soy sauce and soy bread (Giri and Mangaraj, 2012; Orhevba, 2011; Riaz, 2006). Soy products exude beany flavours and astringency that limit acceptance by many consumers from the West (Ogbonna et al, 2013; Silva et al, 2010; Prathap and Ratnavelu 2015). Among the heat treatment techniques, roasting has been reported to offer several advantages such as improvement of colour, shelf life, flavour, digestibility, oil content and reduced anti-nutritional factors
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