NONENZYMATIC BROWNING IN DRIED RED PEPPER PRODUCTS

The nonenzymatic browning of dried red peppers was studied under various water activities, storage temperatures, and packaging atmospheres. Whole pepper and pepper powders-coarse and fine, with and without seeds-were compared. The browning can be described by the zero order reaction, and the rate constant is strongly affected by water activity and temperature. Flushing the package with nitrogen did not have a significant effect on the browning rate. For minimum browning, the peppers should be stored at water activities below 0.3 and in the form of whole pods or coarse powder with seeds.     

SOME REACTION PRODUCTS FROM NONENZYMATIC BROWNING OF GLUCOSE AND METHIONINE

Column and thin-layer chromatographic analysis revealed that acetone, butanal, ethanal, methanal, methional, furfural and 2-propenal were in the monocarbonyl fraction from heat induced glucose and methionine nonenzymatic browning reaction mixtures. Methional was found to be responsible for the characteristic boiled potato-like aroma of the reaction mixture. 2-Propenal was identified as the 3-carbon aldehyde degradation product of methionine.     

CHARACTERIZATION OF THE TEXTURAL PROPERTIES OF SPREADABLE PEANUT BASED PRODUCTS 1

Textural characteristics of two peanut butter samples and one peanut paste sample were determined using three instrumental methods and a texture profile panel. In Method A, a penetrometer with a cone-shaped probe attachment was used. Method B involved the use of a plunger attached to the crosshead of the Instron Universal Testing Machine. Method C was a modified texture profile analysis (TPA). Instrumental measures show that peanut paste was the hardest, exhibited the greatest adhesive force but the least time to break the peanut column, and was the least cohesive. All instrumental methods were acceptable but TPA provided more information than the two other methods in describing texture. The panel rated the paste as firmest, least adhesive, spread least on the tongue, least smooth, most grainy, and most difficult to swallow. Significant correlations were found between several instrumental measures and sensory characteristics.     

CHARACTERIZATION OF BRITTLE FOOD PRODUCTS: APPLICATION OF THE ACOUSTICAL EMISSION METHOD

The structural properties of pasta have been characterized based on sound emisison which generally accompanies rupture of brittle products. This paper presents the principal evolution tendency of the different mechanical and acoustical parameters by varying the relative humidity of the product, and the correlation existing between these two parameters. The correlations suggest that sound emission during rupture may well be utilized to characterize a given product in parallel to or in replacement of commonly measured mechanical properties.     

INFLUENCE OF NONENZYMATIC GLYCOSYLATION (GLYCATION) OF PEA PROTEINS (PISUM SATIVUM) ON THEIR SUSCEPTIBILITY TO ENZYMATIC HYDROLYSIS

The Maillard reaction, also referred to as nonenzymatically glycosylation (glycation), causes changes to protein structure and occurs in food. The aim of this study was to investigate changes in susceptibility of glycated pea proteins to enzymatic hydrolysis. A pea proteins extract was glycated using different sugars (glucose, fructose, lactose and glucosamine). Then, the physicochemical changes of proteins after glycation in ultraviolet spectra as well as the content of sugars and free amino groups were determined and also separated electrophoretically. Native and glycated pea proteins were hydrolyzed for 120 min with pepsin (one-step hydrolysis) or with pepsin and trypsin (in two-step process). Pea proteins glycated by glucose and lactose were less susceptible to pepsin hydrolysis than the pea proteins glycated by fructose and glucosamine in comparison with native pea proteins. Glycated pea proteins were more susceptible to hydrolysis by pepsin and trypsin in the two-step hydrolysis than the native ones.

PRACTICAL APPLICATION

Nonenzymatic glycosylation (glycation) of food proteins is used for the improvement of their functional properties. The formed glycoproteins can be characterized by changing biochemical properties, i.e., the susceptibility to the enzymatic hydrolysis or the influence on the growth and survival of the gut microflora. For this reason, investigations on the effect of the glycation of food proteins on their biological properties were necessary from the nutritional and health-promoting point of view.     

COMPLETE RHEOLOGICAL CHARACTERIZATION OF TIME-DEPENDENT FOOD PRODUCTS

Rheological data are presented for three mayonnaise samples. The material shows pseudoplastic behaviour, and also exhibits a yield stress and time-dependent characteristics. Mayonnaise data are used to demonstrate how the time-dependent behaviour of a food product can be completely characterized using a simplified kinetic and rheological model.     

CHARACTERIZATION OF THE MAILLARD REACTION PRODUCTS OF β-LACTOGLOBULIN GLUCOSYLATED IN MILD CONDITIONS

β‐Lactoglobulin (BLG) was heated in the presence of glucose in mild conditions leading to nonenzymatic glycation through the Maillard reaction. The characterization of the chromophores formed during heating at 60C showed that the modification of the UV‐VIS spectrum of modified proteins was mainly due to a condensation reaction of glucose. Amino acid analysis showed that at least four amino acids (lysine, arginine, histidine and tyrosine) were modified during the reaction. Modification of SDS‐PAGE pattern indicated the prevalence of a covalent polymerization of the BLG monomers independent from disulfide bridge formation Solubility of the glucose ‐β‐lactoglobulin conjugates was higher than that of heated protein at pH 5. A shift of the minimum of solubility toward acidic pH, relative to the shift of the pl of modified proteins, was observed as a function of time of glycation. Tryptic hydrolysis of the modified proteins revealed a slow glycation of Lys 69 as compared to Lys 70, which is consistent with its three‐dimensional orientation and its potential biological role.     

COLORIMETRIC CHARACTERIZATION OF EGG YOLK AND EGG YOLK PRODUCTS

Procedures are suggested for COLOR-EYE® evaluation of various yolk forms and products. Chromaticity coordinates derived from COLOR-EYE determinations and the calculated dominant wavelength (λ_d), excitation purity (P_e) and luminous reflectance (Y_CIE) values were also determined for each yolk form and product analyzed. Characteristics of aged yolks included reduced λ_d and P_e and an increase in Y_CIE values; the greatest effects were at the highest levels of pigmentation concentration. Luminous reflectance values were substantially lowered by the addition of sugar and subsequent frozen storage; all other calorimetric criteria were relatively unchanged. Yolk age effects were negligible for the calorimetric characterization of yolks incorporated into product forms. Mayonnaise products provided the most consistent COLOR-EYE readings. These data suggest the feasibility of utilizing the COLOR-EYE, or similar instrumentation, as an objective method for the color characterization of various yolk products. Numerous options are available for converting data into other desired instrumentation values and terminology.     

STUDIES ON THE INACTIVATION OF LYSOZYME BY MALONALDEHYDE

The interaction of malonaldehyde with lysozyme has been assessed with reference to incubation time, pH, concentration and aging. Gel filtration studies revealed that freshly prepared malonaldehyde contains a small proportion of compounds absorbing at 267 and 350 nm, which shows significant increase upon incubation of malonaldehyde. While higher concentration of malonaldehyde leads to inactivation of enzyme, lower concentration (2.5 mM) stimulates the lytic function of lysozyme. Stimulation and inactivation of the enzyme have been discussed in the context of degradation of malonaldehyde.     

THE ANTIFUNGAL ACTIVITY OF BUTYLATED HYDROXYANIZOLE AND LYSOZYME

The antifungal activity of butylated hydroxyanizole (BHA) and lysozyme alone and combined with ethylenediaminetetraacetic acid (EDTA), at different pH (3.5, 5.6 and 7), and different NaCl concentrations (0.5 to 20%) was screened on 12 fungi. The spiral gradient end point test was used to determine the minimum inhibitory concentration (MIC). BHA was effective against all the fungi tested in the range of < 12 to 460 μg/mL. In the presence of equal amounts of EDTA, the inhibitory effect was amplified (inhibition occurred between < 12 to 200 μg/mL). The inhibition was more pronounced at pH 5.6 and at higher NaCl concentrations especially when EDTA was present. Lysozyme alone was only effective against Fusarium graminearum PM162 and Aspergillus ochraceus MM 184, but was inhibitory for all fungi, except Candida lipolitica 1591, in the presence of EDTA. The inhibition was greatest at pH 5.6 and higher NaCl concentrations, especially when EDTA was present. These studies show that the antifungal properties of lysozyme and BHA can be greatly influenced by environmental factors.     

NONENZYMATIC LIGNIFICATION OF ASPARAGUS?

The hypothesis of nonenzymatic lignification was investigated in asparagus. Samples were stored within 2 h of harvesting at 22C, 4C and - IOC and tested daily, every second day and at 30-day intervals, respectively. Some asparagus was blanched at IOOC for 3 min prior to storage. Assays for peroxiduse and polyphenoloxidase showed no enzymatic activity in the blanched samples. Toughness, as measured by Warner-Bratzler shear force, and crude fiber content (mechanically separated) significantly (P< 0.05) increased in both blanched and unblanched samples over the testing period at all storage conditions. Crude fiber content and shear measurements were significantly (P < 0.05) higher for the enzyme active controls. Microscopic examinations using light (LM) and scanning electron microscopy (SEM) were canied out to locate the site of lignin deposition and to quantify the extent of lignification. Sections viewed using LM techniques were stained to observe useful fluorescence (crystal violet - erythrosin B) and differentiate ligniped from nonlignified cell walls fast green safranin and crystal violet - ertythrosin 8). In samplesfrom each treatment and storage condition, three independent techniques indicated a significant (P < 0.05) increase in: (1) the width of the mechanical tissue layer; (2) the thickness of the cell walls of the cells comprising the mechanical tissue layer, and; (3) the thickness of the xylem vessel walls of the vascular bundles. Also, significant (P C 0.05) differences were detected between the extent of lignification of unblanched and blanched samples. These data suggest that a nonenzymatic "toughening" mechanism does occur in blanched asparagus tissue and that it may be related to lignin deposition.     

CENTRIFUGAL YIELD AND FURTHER MICROSCOPIC CHARACTERIZATION OF SEA BUCKTHORN JUICE PRODUCTS

Yields of press juice for Hippophae rhamnoides ssp. sinensis and ssp. mongolica cv. Indian Summer were 69.2% and 62.8%, respectively. Centrifugation of the press juices at 4C, 4480 × g for 15 min provided yields of cream, serum and pellet of 1.72, 95.6 and 0.68% for ssp. sinensis, and 5.4, 92.3 and 0.32% for ssp. mongolica cv. Indian Summer. All percentages are percentage (w/w). The particulate of each juice was characterized microscopically and the particulate of cv. Indian Summer was much larger than that of ssp. sinensis. Much more oil was apparent microscopically in the cv. Indian Summer cream as expected from the yield data mentioned above. Pellet material was not distinguishable between the two ssp. Trichomes were visualized in greater detail, a particular particle that may be exclusive to cv. Indian Summer was described and the presence of crystalline material in aggregated particles was observed.     

溶菌酶的研究现状

主要阐述了溶菌酶的结构及其性质、种类及其作用机理、提取及制备方法,并讨论了溶菌酶的研究进展.