Preparation Of Different Molecular Weights Of Poly-γ-glutamate And Their Effects On The Quality Of Yogurt And Dough As Addtives

Poly-y-glutamic acid (or y-polyglutamic acid, abbreviated y-PGA) is a natural water-soluble poly-amino acids, it is hydrophilic, biodegradable, no toxic, bio-compatibility, no immunogenicity characteristics. y-PGA can be used as food additives for mineral element absorption agent, thickener, stabilizer, antifreeze agents, with no bad taste. To meet different applications of the y-PGA have different requirements to molecular weight and type of salt ions. Now mainly producer used for y-PGA fermentation was Bacillus strains, the molecular weight of synthesised y-PGA was above 1,000 kDa generally, in actual application it was needed to reform its molecular weight.This work develop y-PGA as a new mineral absorption enhancer and food conditioner, in order to promote the application of y-PGA in food.Acid hydrolysis method was used to decrease high molecular weight of y-PGA fermented by bacteria, according to effects of acid type, temperature and pH on the efficiency and yield of hydrolysis, the method was determined using hydrochloric as hydrolyzing agent at 80℃under the conditions of different pH and hydrolyzing time to prepare different molecular weights of y-PGA. Then, Ultrafiltration was used to desalinate the hydrolyzate, using flux and desalination as an index to choose ultrafiltration membrane, results showed membrane of pore sized be 1/4～1/6 of the target molecular weight cut-off is suitable.Three kinds of molecular weights,600 kDa-800 kDa,300 kDa-400 kDa and 40 kDa-100 kDa, of poly-y-glutamte were prepared, and then studied their effects on yogurt when adding as calcimn chelating agent. Results showed that addition of poly-y-glutamte had no influence on titration acidity and pH; it significantly delayed declining of lactic acid bacteria during storing procedure, and the smaller molecular weight had the better effect, the best was 24.4% higher than that of control in cfu after 14-day’s storage. But, it had adverse effect to centrifugal stability, texture feature and gel characteristics of yogurt, the smaller impact of the smaller molecular weight; For taste,300 kDa-400 kDa molecular weight was relatively the best.Three kinds of molecular weights,1000 kDa-1200 kDa,600 kDa-800 kDa,300 kDa-400 kDa, of poly-gamma-glutamate of Na tape (PGA-Na) and Ca tape (PGA-Ca), were prepared through acid hydrolysis, and then study their effects on wheat dough when adding as food conditioner by farinograph, extensograph, dynamic rheometer and DSC test. This study had clearly shown effects of y-PGA additives varied with cation type and molecular weight on dough were different.1000 kDa-1200 kDa PGA-Na had the best effect on farinograph characteristics, while 300 kDa-400 kDa PGA-Na had greater improvements for extensograph characteristics and antifreeze activity. To the gel properties during pasting progress,600 kDa-800 kDa PGA-Ca was the best in using.