Factors affecting the acid gelation of sodium caseinate

Acid gelation, turbidity and particle size development of dispersions of sodium caseinate and other protein fractions were studied. Sodium caseinate dispersions became particulate prior to the onset of gelation. Casein particles had enhanced stability to gelation in the presence of sodium chloride. Removal of the hydrophilic part of the κ-casein molecule through renneting and acidification of the soluble sodium para-caseinate resulted in increased gelation pH. Removal of most of the κ-casein through ethanol fractionation of sodium caseinate resulted in an α_s1-β-fraction, which was markedly destabilised at higher pH values during acidification in the presence of sodium chloride. Preheated β-lactoglobulin/sodium caseinate dispersions had similar acid gelation profiles in the presence of sodium chloride with or without N-ethylmaleimide, suggesting that secondary thiol-disulphide interchange reactions between κ-casein and pre-heated β-lactoglobulin aggregates did not effect the gel point and final storage modulus in the short time-frame (120 min) of acidification. It was found that κ-casein and sodium chloride played a significant role in both particle development and subsequent stability of sodium caseinate dispersions on acidification.     

Production of phage free cheese whey: Design of a tubular laboratory membrane filtration system and assessment of a feasibility study

An interposed “phage filtration” process step is proposed prior to subsequent processing of cheese whey to whey products to reduce fermentation risks due to phage contamination. At laboratory scale, the characteristics of three single tube ceramic membranes on the filtration performance in terms of phage retention, protein transmission and filtrate flux were analysed. From these tested membranes, a 0.1 μm microfiltration membrane was found to be suitable for significant phage reduction (3.4 log units) in cheese whey, simultaneously allowing total protein transmission of 56.2%. The experiments within the designed feasibility study conducted with a pilot plant microfiltration system provided a higher phage retention (4.1 log units) and a significantly increased transmission of major whey proteins (up to 84%) in comparison with the laboratory plant. The results shown in this study can easily be adapted by the dairy industry for better phage control and enhanced process safety.     

Effect of calcium reduction on the properties of half-fat Cheddar-style cheeses with full-salt or half-salt

Standard-calcium (SCa) and reduced-calcium (RCa) half-fat (16%) Cheddar-style cheeses with full-salt (1.9%) or half-salt (0.9%) were made in triplicate, ripened for 270 d, and analysed for composition and changes in lactose metabolism, pH, proteolysis, water-sorption, fracture properties and heat-induced flowability during maturation. The pressing load applied to the moulded cheese was modified to ensure equal moisture in all cheeses despite the differences in salt and calcium levels. The RCa cheeses were characterised by higher primary proteolysis (α_S1-casein degradation, pH 4.6-soluble N development), lower secondary proteolysis (concentration of free amino acids), higher water-holding capacity on reducing relative humidity from 85 to 5%, lower fracture stress and strain, and more extensive flow on heating. Overall, calcium reduction, when used in conjunction with moisture normalisation, proved an effective means of counteracting the adverse effects of fat reduction on texture and cooking properties in half-fat, half-salt cheese.     

Does waiving preventive food control inspections in Finland weaken the prerequisites for safe food handling in restaurants?

Finnish food control authorities waived pre-inspections of food premises in 2011, leaving food business operators to begin operating with no pre-operation food control. This study aims to investigate the effects of this food policy change on the preconditions for Good Hygienic Practices (GHPs) on food premises. Of the 916 food premises that were included in this study, 379 were pre-approved whereas 537 merely notified their operations. The results show that notified food service premises (restaurants) preparing food displayed significantly more non-compliance pertaining to infrastructure than did restaurants pre-approved for food preparation (11.5% and 1.8% of the premises, respectively) (p < 0.05). Significant differences also emerged in the number of premises with non-compliance pertaining to cleaning facilities and equipment, and marked differences in the adequacy of hand and other washing sites. Such instances of non-compliance weaken the preconditions for GHPs. The results suggest that re-introducing pre-inspections of restaurants would strengthen the preconditions for GHPs and possibly provide a model for other countries with similar food control systems.     

Study of taste-active compounds in the water-soluble extract of mature Cheddar cheese

The chemical composition of the water-soluble extracts of mature Cheddar cheese were identified, with the emphasis on understanding the interplay of compounds contributing to the savoury taste in Cheddar. The ultra-filtered water-soluble extracts of two mature Cheddar cheeses were fractionated by gel permeation chromatography (GPC). By sensory evaluation, two taste-active GPC fractions were identified from each cheese. On the basis of chemical profiling of these fractions, aqueous model tastant mixtures were prepared and sensory omission tests carried out. Glutamic acid, organic acids and mineral salts were the main tastants, whereas the other amino acids had a limited impact on taste. The characteristic umami taste was explained by a synergistic effect of glutamic acid and salts. Matching umami taste intensities were obtained from different concentrations of glutamic acid and salts. Unmasking of a bitter or sweet taste from mixtures of sub-threshold concentrations of amino acids without glutamic acids was also observed.     

Surveillance of listeriosis and its causative pathogen,Listeria monocytogenes

To manage the problem of foodborne listeriosis requires an understanding of the burden of the disease on a worldwide scale as foods that are prone to contamination are eaten widely domestically and many are traded globally. Surveillance of the disease, caused by Listeria monocytogenes, is typically restricted to developed countries, but many of these do not consider listeriosis as a notifiable disease and estimate the numbers by other means. Incidence rates range from 0.3 to 1.3 per 100,000, but most are in the 0.3–0.5 range, irrespective of the regulatory system and industry control programmes that have been in place. Ready-to-eat foods are the vehicle for transmission of the Listeria through contamination somewhere in the food chain. Meat, poultry and dairy products have been most frequently implicated, but other foods including produce may also have been vehicles of transmission. Large outbreaks are usually linked to errors in food processing plants, such as contaminated slicing machines, followed by opportunities for growth of the pathogen. Less is known about home-generated illnesses but incorrect use of refrigerators can allow cross-contamination and growth of the pathogen to levels that can cause infections. In the U.S., door-to-door salesmen have sold contaminated Hispanic soft cheeses that have led to outbreaks and stillbirths. In addition to outbreak investigation, case-control studies, and the use of experts, risk assessments, and food attribution studies can help focus on areas of greatest risk for prevention and control measures throughout the food chain.     

In vitro antifungal activity of lactic acid bacteria against mycotoxigenic fungi and their application in loaf bread shelf life improvement

Food spoilage caused by mycotoxigenic fungi represents an important food safety problem. Lactic acid bacteria (LAB) are used as starter cultures in a larger number of food products. In this study, 16 strains of LAB were cultivated in MRS broth under anaerobiosis. Then, cell free supernatants were obtained by centrifugation and their antifungal activity against Aspergillus parasiticus and Penicillium expansum was tested using the disc-diffusion method. Furthermore, the LABs that showed in vitro antifungal activity were used in bread fermentation with yeast in order to study fungal growth inhibition and aflatoxin (AF) reduction in processed bread previously inoculated with A. parasiticus. The compounds present in the fermented medium of six LAB strains induced inhibition of P. expansum growth, whereas five probiotic strains produced antifungal compounds against A. parasiticus. The analysis by liquid chromatography coupled to mass spectrometry in tandem showed a reduction of the AF content in bread samples fermented with yeast and LABs. The reduction of AFs ranged from 84.1 to 99.9%. Moreover, bread sample studies showed a shelf life increase of about 3–4 days.     

In-house method validation,estimating measurement uncertainty and the occurrence of fumonisin B1 in samples of Brazilian commercial rice

Fumonisin B₁ was investigated in samples of rice intended for human consumption, including polished parboiled rice, whole grain rice and whole grain parboiled rice. Until the present, no studies on the occurrence of fumonisin B₁ have been performed on these types of rice that are commercially available in the south-eastern region of Brazil. A careful intralaboratory validation was carried out to demonstrate the fitness-of-purpose of the applied method for determining fumonisin B₁ in the three studied rice types. The performance criteria – selectivity, reliable limits of detection (50 μg kg⁻¹) and quantification (100 μg kg⁻¹), linearity (range 100–2500 μg kg⁻¹), precision (RSD values ≤ 17.0%) and recovery (71.7–112.0 %) were evaluated, and the expanded measurement uncertainty was estimated by using the data obtained from precision and recovery experiments. Matrix-matched calibration standards were employed to quantify the mycotoxin levels in the rice samples, in which the residual normality, homoscedasticity and independence were confirmed. In addition, the measurement uncertainty values are consistent with the maximum acceptable uncertainty established by European Union regulation for analytical methods for controlling mycotoxins in foodstuffs. Among the thirty-one commercial samples of rice analysed in the present study, five samples presented detectable levels of the mycotoxin, and these levels ranged from 64.8 to 163.0 μg kg⁻¹.