PROTEIN-PHYTATE INTERACTIONS IN SOYBEANS. II. MECHANISM OF PROTEIN-PHYTATE BINDING AS AFFECTED BY CALCIUM

Phytate and bovine serum albumin were used in a model system to investigate the mechanism of their binding. Ultrafiltration studies using response surface design showed the association of protein and phytic acid to be highly pH dependent. Under acid conditions, the protein formed an insoluble complex with phytic acid. At pH 3.0, a binding constant of 2.3 times 10⁵ was obtained and it was calculated that there are 78 binding sites of the total 93 basic amino acid residues potentially available. This low pH complex was not disrupted at high temperatures but the presence of calcium ions caused dissolution of the precipitate. Calcium produced different effects at higher pH (> 6). Soluble protein-calcium-phytic acid complexes were formed which were less stable to heat and dissociated above pH 10 at high ionic strength. Since this interaction occurred only in the presence of calcium, a salt linkage is implicated in which divalent cations simultaneously bind to the protein and phytic acid in the form of a soluble complex. It is proposed that either the addition of divalent cations at low pH or sequestering agents at high pH would best effect the removal of phytate from soy products by ultrafiltration.     

PROTEIN-PHYTATE INTERACTIONS IN SOYBEANS. I. LOCALIZATION OF PHYTATE IN PROTEIN BODIES AND GLOBOIDS

A study was made of whole soybeans, isolated protein bodies and a fraction consisting of globoid inclusions separated from protein bodies by centrifugation in order to observe the cellular location of phytate and to determine any indication of protein-phytate interaction within the soybean cell. Microstructural and chemical evidence demonstrated phytic acid to be located in the protein bodies of the soybean, likely in the form of a soluble protein-phytate salt with significant amounts specifically deposited in globoid inclusions. The probable existence of a protein-cation-phytate complex in situ was shown by gel filtration in which calcium and phosphorus was found to coelute with soluble proteins. The proteins involved in this interaction were tentatively identified as the 7S soybean fraction.     

EFFECT OF HEATING TEMPERATURE AND MICROWAVE PRETREATMENT ON THE FORMATION OF SUGARS AND VOLATILES IN JEWEL SWEETPOTATO

Experiments investigating changes in the concentration of individual sugars in sweetpotato storage roots with cooking and their relationship to the formation of volatile compounds were conducted. During heat treatment maltose concentration increased from 0.03% fresh weight at 25C to 4.33% at 80C, at which temperature maximum synthesis occurred. Microwave pretreatment (2 or 4 min) resulted in a significant decrease in amounts of maltose and volatiles formed. At 80C, approximately 80% of maltose synthesis was inhibited when pretreated With microwaves. Adding maltose into microwave pretreated samples and then cooking in a convection oven restored most of the volatile profile with the exception of phenylacetadelhyde. It was concluded that maltose represents a primary precursor for many of the volatile compounds emanating from baked ‘Jewel’ sweetpotatoes and the formation of these volatiles appears to involve both enzymatic and thermal reactions.     

N-Nitrosamine Analysis in Beer Using Thermal Desorption Injection Coupled with GC-TEA

A fast and sensitive method is described for determining a mixture of volatile N-nitrosamines in beer and other malt products. It consists of direct extraction of the sample with dichloromethane, volume reduction, cleanup by trapping volatiles onto Tenax-TA, and thermal desorption injection into a capillary gas chromatograph-thermal energy analyzer. Average recovery of N-nitrosodimethylamine added to beer ranged from 70 to 81%. N-Nitrosodimethylamine and N-nitrosopyrrolidine were detected in 10 samples of various domestic and imported beers analyzed. Total volatile N-nitrosamine concentrations ranged from 0.03 to 1.10 ppb in beer. Minimum detection limit of the method was 0.01 ppb for N-nitrosodimethylamine, a 10-fold increase in sensitivity compared to other similar methods.     

PREDICTING MEAT TENDERNESS FROM MUSCLE TENSILE PROPERTIES

Two major types of objective measurements were performed on raw porcine psoas muscle (I - shearing and breaking strength tests; II - sarcomere length, elasticity, stress relaxation and break elongation) and compared with taste panel evaluation (tenderness, elasticity, and chew count) of cooked meat. A standard sample of texturized vegetable protein used as a reference by the panel proved useful in reducing variations between the chew count test and the objective evaluation; it was not of significant value with the other sensory evaluations. No significant correlations were found between the two groups of objective measurements. Breaking strengths of small longitudinal strips of tissue, following a brief cyclic or extension stretching on the Instron, were the best predictors of sensory tenderness accounting for 59–90% of variation. Other measurements also gave significant correlations. The major source of variation in breaking strength values was the variation between animals, but the post-mortem treatment (restraining versus not restraining during rigor) and the interaction between animals and the post-mortem treatment also were significant in some cases. Breaking strengths of uncooked samples from the same muscle showed a coefficient of variation of up to 54%. It is concluded that there are two major structural contributions of raw muscle to cooked meat tenderness, a connective tissue factor and a contraction factor; different objective methods are best suited for their evaluation.     

SOME CHARACTERISTICS OF EFFECTIVE INTERVIEWERS.

SAMPLE ADDRESSES WERE SELECTED ON A PROBABILITY BASIS FROM THE RECORDS OF FINANCIAL INSTITUTIONS AND THE HOLDINGS REPORTED TO THE INTERVIEWER WERE COMPARED WITH INSTITUTION RECORDS FOR THE DAY OF THE INTERVIEW. THE FREQUENCY WITH WHICH AN INTERVIEWER OBTAINED INFORMATION ABOUT THE VALIDATED ACCOUNT(S) FORMS THE BASIS FOR THE CRITERIA OF INTERVIEWER EFFECTIVENESS. IT WAS FOUND THAT THE MORE EFFECTIVE INTERVIEWERS SCORED SIGNIFICANTLY HIGHER ON THE DOMINANCE AND INTRACEPTION TESTS AND LOWER ON THE SUCCORANCE AND CHANGE TESTS OF THE EPPS. IN ADDITION, THEY SCORED SIGNIFICANTLY HIGHER IN REFERENCE EVALUATIONS OF SELF-CONFIDENCE AND ATTENTION TO DETAIL. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of Polyphosphate on Storage Stability of Restructured Beef and Pork Nuggets

Influence of polyphosphate on sensory and chemical characteristics of battered and breaded, cooked, restructured beef and pork nuggets was evaluated over 20 wk storage. Beef and pork nuggets manufactured with polyphosphate had lower (P<0.05) initial thiobarbituric acid (TBA) values than those manufactured without polyphosphate (controls); and values remained lower (P<0.05) than control treatments over 20 wk of storage. Sensory panelists detected less (P<0.05) off-flavor in pork nuggets manufactured with polyphosphate than nuggets in control treatments. Detection of off-flavor in pork nugget control treatments may be attributed to higher TBA values (increased lipid oxidation) in the pork product. Addition of polyphosphate protected nuggets from lipid oxidation and subsequent off-flavor development.