PHYTIC ACID HYDROLYSIS AND BEAN SUSCEPTIBILITY TO STORAGE INDUCED HARDENING1

Two bean cultivars were stored over a 33-day period (75% RH and 41°C). After this period, cooked hardness, levels of phytate, phytase activity and integrity of protein bodies were monitored. The Michigan cultivar, which was the most susceptible to hardening, showed higher initial content of phytate which decreased by 20.7% after 30 days of storage. In contrast, Ojo de cabra, the cultivar less susceptible to hardening, presented lower initial content of phytate and a marked drop of 66.1% in its level during the same period of time. The phytase activity and the autolytic protein body destruction were higher in the last one than those in the former one. These results suggest that the contents of phytate or its rate of hydrolysis are not the major contributor to the seed susceptibility to storage induced hardening of different bean varieties.     

Production of low-fat Chanco cheese using homogenized milk and adjunct lactic culture

The objective of this study was to determine the effect of the partial homogenization of milk and the use of an adjunct lactic culture on the processing, quality and yield of low-fat Chanco cheese.
  Treatments were: T1 normal-fat control and T2 low-fat control. The low-fat treatments were: T3 using homogenized milk, T4 with adjunct lactic culture and T5 both variables.
   It was concluded that the homogenization slightly increased the time of rest after cutting of the curd, and the addition of adjunct lactic culture increased the acidity of whey during a second agitation. Nevertheless, the total time and pH at the end of the process were normal and without significant statistical difference ( P  > 0.05) between treatments. When using homogenized milk the losses of fat in whey decreased by 50% with respect to the low-fat control and nearly 80% in relation to the full fat control. Consequently, the yield was increased. The physical and chemical characteristics of the Chanco cheese were not affected by the studied variables. With respect to the sensory evaluation, significant differences in colour and aroma did not appear, but there were statistically significant differences (P <  0.05) in taste, hardness, adhesiveness, cohesiveness and elasticity between the full-fat control and all the low-fat treatments. In the case of general acceptance, the treatment with adjunct lactic culture was similar to the full-fat control. In addition, it showed the least difference (mild) in elasticity and taste in relation to this control .     

Usability perceptions and beliefs about smart thermostats by chi-square test,signal detection theory,and fuzzy detection theory in regions of Mexico

It is well known that smart thermostats (STs) have become key devices in the implementation of smart homes; thus, they are considered as primary elements for the control of electrical energy consumption in households. Moreover, energy consumption is drastically affected when the end users select unsuitable STs or when they do not use the STs correctly. Furthermore, in future, Mexico will face serious electrical energy challenges that can be considerably resolved if the end users operate the STs in a correct manner. Hence, it is important to carry out an in-depth study and analysis on thermostats, by focusing on social aspects that influence the technological use and performance of the thermostats. This paper proposes the use of a signal detection theory (SDT), fuzzy detection theory (FDT), and chi-square (CS) test in order to understand the perceptions and beliefs of end users about the use of STs in Mexico. This paper extensively shows the perceptions and beliefs about the selected thermostats in Mexico. Besides, it presents an in-depth discussion on the cognitive perceptions and beliefs of end users. Moreover, it shows why the expectations of the end users about STs are not met. It also promotes the technological and social development of STs such that they are relatively more accepted in complex electrical grids such as smart grids.     

Influence of cephalosporins on the coagulation time of yogurt made from ewes’ milk

Ceftiofur and cephalexin were independently added to ewes’ milk at three different concentrations 50, 100 and 150 µg/kg. Spiked milk was used to produce yogurt and the acidification of the yogurt during incubation was then studied. Ceftiofur showed significant delays in the pH decrease rate at all concentrations assayed, but no significant delays occurred with cephalexin. When these antibiotics were administered intramuscularly to lactating ewes, from which the milk was used to make yogurt immediately after the corresponding withdrawal periods, absence of residues and pH delays were not observed during the yogurt fermentation in the presence of any antibiotic.     

OXIDATION OF INDOLEACETIC ACID BY AN APPARENTLY HOMOGENEOUS PEROXIDASE FROM THE FLAVEDO OF WASHINGTON NAVEL ORANGES (CITRUS SINENSIS)

Orange flavedo peroxidase was purified by ammonium sulfate fractionation, gel filtration and ion-exchange chromatography. The anionic fraction, representing 51% of the total peroxidase activity, was an apparently homogeneous isoenzyme with an pI of 4.0. The cationic fraction was composed of two isoenzymes with pI of 10.0 and 11.5.
The anionic peroxidase oxidized indoleacetic acid in the presence of H₂O₂ and 2,4-dichlorophenol. This reaction was inhibited by Mn²⁺ and enzyme activity decreased at increasing pH in the range of 4.0 to 5.5. This isoenzyme also oxidized indoleacetic acid in the reaction mediated by 2,4-dichlorophenol, Mn²⁺ and phosphate. In this case the optimum pH was 4.5 and the reaction was inhibited by H₂O₂.
Study of the characteristics of both reactions indicates that, even though they could share some common steps and have similar end products, they probably differ in their reaction mechanism. The possible physiological significance of the H₂O₂ mediated oxidation of indoleacetic acid is briefly discussed.     

Queso Chihuahua: effects of seasonality of cheesemilk on rheology†

Fresh semihard raw milk (RM) and pasteurized milk (PM) cheeses made by Mennonite communities in Chihuahua, Mexico were sampled in early winter, mid‐spring and late summer and evaluated during storage to determine if rheological properties were affected by the season the cheese was produced. Seasonal effects were observed in the rheology of the RM cheeses, which underwent more extensive proteolysis than the PM cheeses. The rheological properties of the PM cheeses and the composition of all cheeses were consistent throughout the year. The texture of the RM cheese is affected by season, whereas the variability in texture and composition of PM cheese is minimal, allowing for the manufacture of a uniform product.     

Detection of Proteolytic Activity in Microorganisms Isolated from Dry-Cured Ham

Different assays were tested for the detection of proteolytic activity in both Pediococcus pentosaceus and Staphylococcus xylosus, two major microorganisms isolated from dry-cured ham. Absence of endopeptidase activity was found even when using raw sarcoplasmic and myofibrillar proteins. However, P. pentosaceus showed strong leucine and valine arylamidase activities while St. xylosus showed a very weak leucine arylamidase activity.     

Relationship between A and B variants of κ-casein and β-lactoglobulin and coagulation properties of milk (Part II)

The purpose of this study was to relate the genetic variants A and B of κ-casein (κ-CN) and β-lactoglobulin (β-Lg) of the milk of 10 Chilean Holstein–Friesian cows and its coagulation properties (coagulation ability of milk, curd firmness and syneresis of the curd).
The results showed that β-Lg AB phenotypes have a significant effect on the studied properties in comparison with the samples containing the AA phenotype. A and B variants of κ-CN did not have a significant effect on the coagulation properties, although there was a favourable interaction between β-Lg AB and κ-CN B.