An in vitro method using a multienzyme system for the estimation of protein digestibility has been developed. The multienzyme system consists of trypsin, chymotrypsin and peptidase. It was found that the pH of a protein suspension immediately after 10 min digestion with the multienzyme solution was highly correlated with the in vivo apparent digestibility of rats. Regression analyses of 23 samples tested showed that the correlation coefficient between pH at 10 min and in vivo apparent digestibility was 0.90 with a standard error of estimate of 2.23. The regression equation was Y = 210.464 -18.103, where "X" was the pH of protein suspension immediately after the 10 min digestion with the multienzyme solution. The most significant advantage of this in vitro method for predicting apparent protein digestibility was that it can be completed within 1 hr and with a high degree sensitivity. The method can detect the effects of trypsin inhibitor, chlorogenic acid, and heat treatment on protein digestibility. Strong buffer salts may affect the measurement of protein digestibility, but the buffering effects found in general food proteins and products tested did not create any problem with the procedure.

Leaf protein concentrate (LPC) haa been shown to have the phenolic acid, chlorogenic acid, bound to its protein molecules. Bound chlorogenie acid creates off color problems in foods containing LPC as an ingredient and also possibly lowers the digestibility of LPC by inhibiting the rate of trypsin attack on the protein. A buffer, containing 2.5% NaCl-1 mM mercaptoethanol-40 mM phosphate, effectively removed 69% of the chiorogenic acid from LPC. LPC, with the majority of its chlorogenic acid removed, had an enhanced in vitro protein digestibility and an amino acid pattern very similar to that of the original LPC. A series of small molecular weight proteins were found to be the chlorogenie acid binding fraction in LPC.

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The purpose of this research was to ascertain the nature of the material in granulated cane sugar which causes flocculation in acidified sugar syrups, and is, consequently, undesirable in bottled beverages. The acid and alcohol floes of 12 sugar samples were examined for their amino acid content. Floccing sugars contained a higher concentration of amino acids than nonfloccers. Isolation techniques were developed for the floe-causing substance (FCS) using ion-exchange column chromatography. Characterization studies indicate that the FCS is primarily degradated amylose which is believed to be the nucleus of an aggregation. The nature of proteins, peptides and other substances in forming the complex is not clear.

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