Liquid milk has been an important human nutrient source for a thousand years. However, the safety of milk has always been challenged due to illegal use of preservatives and adulterants such as hydrogen peroxide, salicylic acid, benzoic acid, water, neutralizers, melamine, and so on. Downloaded by [Selcuk Universitesi] at 05:28 03 February 2015A c c e p t e d M a n u s c r i p t 2 Addition of these two types of substances in milk has become a common feature for fulfilling the milk demands of over-populated countries. Now, for the dairy industry, it seems to be difficult to run the plant without the use of preservatives and or adulterants especially under Indian conditions. In addition to their potential toxic effects on human health, they also undermine the economy of a country. The lack of timely action against the unscrupulous traders by the Public Health Departments and other law enforcement groups, and lack of simple and rapid methods for detection of adulteration further encourage this menace. This overview attempts to address the key features of these two types of harmful substances in milk, their effect on milk composition and constituents along with their regulatory and safety aspects.

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The purpose of this study is to investigate the effect of twin‐screw extrusion conditions on the properties and quality attributes of corn starch (CS) and potato starch (PS). Extrusion processing conditions used are—feed moisture level of 17% and 18%, screw speed level of 414 and 533 rpm, and barrel temperature of 131 and 135 °C for CS and PS, respectively. When compared with native starches, it is demonstrated that extrusion has a positive effect on the functional properties, that is, bulk density decreases, but water absorption index, water solubility index, degree of gelatinization, and in vitro digestibility increase significantly, and transform its native structure to a honeycomb‐like fine meshwork. Extrusion also results in a significant decrease in pasting temperature, peak viscosity, hold viscosity, final viscosity, breakdown viscosity, and setback viscosity of both the starches. In color profile, a decrease in luminosity, but increase in redness and yellowness are observed in extruded starches. Scanning electron microscopy and X‐ray diffractometry studies show that extrusion leads to complete destruction of structure along with reduced crystallinity and formation of V‐type polymorphs in starches. Compared to CS, PS shows more surface protrusions and formation of air cells leading to formation of a much more microporous structure.

Extrusion cooking studies were carried out with a view to develop an instant porridge from wheat grits and guava pulp at different levels from 10 to 50 %. The mixtures were dried to bring down the moisture content to 12, 15 or 18 % and processed using twin screw extruder. The properties of extrudates (expansion ratio and density) and porridge (water absorption index, water solubility index and sensory quality) were studied. Increase in feed moisture content and guava pulp level resulted in the decrease in expansion ratio and increase in density of the extrudates. Water absorption index (WAI) increased and water solubility index (WSI) decreased with increase in feed moisture content. With increase in level of pulp, WAI decreased and WSI increased. Highly acceptable porridge was obtained at 15 % feed moisture content and 20 and 30 % guava pulp. To the samples with selected feed moisture and pulp levels, sugar was added at 20, 25 and 30 % levels to prepare the final product. Sugar level of 30 % was found out to be most acceptable. Fruit porridge stored in LDPE and aluminum laminate pouches at ambient temperature remained acceptable upto 6 months.

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Undesired browning of Parmesan cheese can occur during the latter period of ripening and cold storage despite the relative absence of reducing sugars and high temperatures typically associated with Maillard browning. Highly reactive α-dicarbonyls such as methylglyoxal (MG) are products and accelerants of Maillard browning chemistry and can result from the microbial metabolism of sugars and AA by lactic acid bacteria. We demonstrate the effects of microbially produced MG in a model Parmesan cheese extract using a strain of Lactobacillus casei 12A engineered for inducible overexpression of MG synthase (mgsA) from Thermoanaerobacterium thermosaccharolyticum HG-8. Maximum induction of plasmid-born mgsA led to 1.6 mM MG formation in Parmesan cheese extract and its distinct discoloration. The accumulation of heterocyclic amines including β-carboline derivatives arising from mgsA expression were determined by mass spectrometry. Potential MG-contributing reaction mechanisms for the formation of heterocyclic amines are proposed. These findings implicate nonstarter lactic acid bacteria may cause browning and influence nutritional aspects of Parmesan by enzymatic conversion of triosephosphates to MG. Moreover, these findings indicate that the microbial production of MG can lead to the formation of late-stage Maillard reaction products such as melanoidin and β-carbolines, effectively circumventing the thermal requirement of the early-and intermediatestage Maillard reaction. Therefore, the identification and control of offending microbiota may prevent latestage browning of Parmesan. The gene mgsA may serve as a genetic biomarker for cheeses with a propensity to undergo MG-mediated browning.Accurate mass was determined by liquid chromatography (LC) electrospray ionization time-of-flight (Agilent 1969A, Agilent Technologies, Santa Clara, CA). The mass to charge ratio (m/z) of fragment ions and their relative intensity were generated using a collision energy of 40 eV and determined by LC-MS/MS (Sciex QTRAP 5500, Sciex, Framingham, MA). Figure 3. Liquid chromatography tandem mass spectrometry (LC-MS/MS) comparison between β-carboline derivatives formed in Parmesan cheese extract (PCE) from Lactobacillus casei 12A expressing methylglyoxal synthase (mgsA) and 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (THβCA) and Harman. (A) Compound 4 and THβCA, and (B) compound 6 and Harman. The mass to charge ratio (m/z) of fragment ions and their relative abundance in samples and commercially available standards were generated using a collision energy of 40 eV and detected by LC-MS/MS (Thermo TSQ Quantum Discovery Max, Thermo Fisher Scientific, Waltham, MA). The co-elution profile of the compound and standard is depicted in the upper right-hand corner of each mass spectrum.

Endogenous production of α-dicarbonyls by lactic acid bacteria can influence the quality and consistency of fermented foods and beverages. Methylglyoxal (MG) in Parmesan cheese can contribute toward undesired browning during low temperature ripening and storage conditions, leading to the economic depreciation of affected cheeses. We demonstrate the effects of exogenously added MG on browning and volatile formation using a Parmesan cheese extract (PCE). To determine the influence of Lactobacillus on α-dicarbonyls, strains were screened for their ability to modulate concentrations of MG, glyoxal, and diacetyl in PCE. It was found that a major metabolic pathway of MG in Lactobacillus is a thiol-independent reduction, whereby MG is partially or fully reduced to acetol and 1,2-propanediol, respectively. The majority of lactobacilli grown in PCE accumulated the intermediate acetol, whereas Lactobacillus brevis 367 formed exclusively 1,2-propanediol and Lactobacillus fermentum 14931 formed both metabolites. In addition, we determined the inherent tolerance to bacteriostatic concentrations of MG among lactobacilli grown in rich media. It was found that L. brevis 367 reduces MG exclusively to 1,2-propanediol, which correlates to both its ability to significantly decrease MG concentrations in PCE, as well as its significantly higher tolerance to MG, in comparison to other lactobacilli screened. These findings have broader implications toward lactobacilli as a viable solution for reducing MG-mediated browning of Parmesan cheese.

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