Molecular Weight Distribution of Protein Hydrolysate by the Enzymic Hydrolysis of Weakly Acid-Treated Wheat Gluten

Abstract

For the production of highly soluble HVP (hydrolysed vegetable protein) by enzymic hydrolysis, wheat gluten suspension (6% w/w, protein) was pretreated with weak acid (0.1 N HCl) at 95°C for 1 h to overcome insolubility of the suspension. After treating it for 3 h with alcalase, flavourzyme was added to the wheat gluten hydrolysate and hydrolysis continued for a further 21 h at 50°C. ␣-Amino nitrogen content (AN, mg/ml) and nitrogen solubility index (NSI, %) of the resulting wheat gluten hydrolysate product was 2.87 mg/ml and 94.9%, respectively. The wheat gluten hydrolysate product contained peptides and free amino acids with molecular weights below 300 dalton. Non-acid treated SPI (soy protein isolate) was also adopted as a protein substrate. The AN and NSI of the resulting SPI hydrolysate were 2.02 mg/ml and 70.4%, respectively. SPI hydrolysate contained proteins and peptides with molecular weights above 80 Dalton and below 7300 Dalton.Keywords: protein hydrolysate, wheat gluten, SPI, enzymic hydrolysis By partial hydrolysis of proteins, characteristics including the functional properties of solubility, foaming capability, emulsion stability and flavouring agent formation can be created or enhanced. Moreover, hydrolysis can be performed to suppress the formation of undesirable and complex odors and colors, as well as to eliminate toxic and anti-nutritional components. The protein hydrolysis is conducted by chemical methods of acid or alkaline treatments and also by various proteolytic enzymes (Lahl & Braun, 1994). For the purposes mentioned above acid hydrolysis can be easily applied in general, but it often causes not only undesirable tastes and odors, but also the loss of essential amino acids, the reaction with non protein substances and the formation of lysinoalanine which limits the use of proteins (Deeslie & Cheryan, 1981, Finley et al., 1982. Acetylation (Franzen & Kinsella, 1976, Kim & Rhee, 1989 and phosphorylation (Kim et al., 1988) treatment of proteins also have some safety problems. Recently in Korea, soy sauce produced by hydrochloric acid treatment has become one of the great social issues due to the formation of the toxic compounds such as MCPD (3-chloro-1,2-propanediol) and DCP(1,3-dichloro-2-propanal) (Velisek et al., 1978, 1980, Rillaer & Beernaert, 1989, Bergen et al., 1992. These can be formed by 5.0-9.5% lipids found in vegetable proteins, such as mono-, di-, triglycerides, phospholipids and glycolipids during reactions with high concentrations of hydrochloric acid at high temperature and long reaction times. Hamm (1992) proposed weak acid pretreatment of wheat gluten and soy protein isolate for the subsequent enzymic hydrolysis to suppress the formation of MCPD and DCP. Recently preferred enzymic hydrolysis of proteins has several difficulties, especially in the process of high protein concentrations and in achieving a high degree of hydrolysis, as well as microbial contamination during long reaction time compared to acid hydrolysis (Lin & Lee, 1987). In order to achieve economic feasib...

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