Papers by Muhammad Gulzar
Food Research International, 2013
In the present work, we investigated the structural modifications occurring during the dry heatin... more In the present work, we investigated the structural modifications occurring during the dry heating of model whey proteins, β-lactoglobulin and α-lactalbumin. Samples were adjusted to pH 6.5, water activity a w = 0.23 and dry heated at 100°C for up to 24 h, and the structural modifications followed by gel permeation chromatography, reverse phase-HPLC, SDS PAGE and mass spectrometry (LC-MS/MS). The dry heating treatment traps a fraction of the proteins into covalently linked soluble aggregates. Moreover, a high proportion of non-aggregated α-lactalbumin (about 73%) was converted into non-native forms. The characteristic of those non-native species was the loss of one or two water molecules per α-lactalbumin molecules. Using tandem mass spectrometric peptide mapping, these chemical modifications were found to be attributed to (i) the formation of a pyroglutamic acid from the N-terminal glutamic acid and (ii) the formation of an internal cyclic imide at position Asp 64 . The non-native species were not favored in the case of β-lactoglobulin as they represented less than 18% of non-aggregated proteins.
Journal of Animal and Plant Sciences
The quality of fermented dairy products is a delicate subject. In addition to processing conditio... more The quality of fermented dairy products is a delicate subject. In addition to processing conditions, it largely depends on pre and post process handling. The present study is concerned with the physicochemical and microbiological quality of commercially available yogurt in Faisalabad, Pakistan. For this purpose, two branded (produced at large scale) and three unbranded (produced at small scale) yoghurt samples were collected from the city and were analyzed in triplicate. The data was analyzed by complete randomized design (1-factor factorial) and comparison of means was done by Duncan's multiple range test. The coliform count in branded samples was nil or ignorable. However, unbranded samples contained a higher count of coliforms. The branded samples were monocultured (S. thermophilus), which does not fulfill the quality criteria as L. bulgaricus is also needed for good quality yoghurt. In contrast, in unbranded samples, both the bacteria were present but their growth was uncontrolled. The fat, lactose and total solid contents were low in unbranded yoghurt samples than in branded samples showing lack of standardization. However, acidity and syneresis value of branded samples were low as compared to unbranded samples.
Functional foods containing probiotic bacteria (lactic acid bacteria and bifidobacteria) are gett... more Functional foods containing probiotic bacteria (lactic acid bacteria and bifidobacteria) are getting popularity in the world, due to tremendous health benefits conferred by these bacteria. However, the total viable count of bacteria in the final product and the sensory attributes of the product are of higher importance for its consumer acceptability. In this study, flavored (strawberry, pineapple, and mango) probiotic acidophilus milk (from buffalo) using probiotic starter culture (Lactobacillus acidophilus) was prepared and its microbiological, physicochemical and sensory quality studies were carried out up to 6 days of storage. A slight increase in acidity of the milk was observed after 6 days of storage resulting in a decrease of pH (from pH 4.5 to 4.3). Total viable count of L. acidophilus bacteria was decreased after 6 days of storage due to increase in acidity but it was still within acceptable range (>10(6)). Sensory evaluation data shows that the quality of sensory attrib...
Heat-induced denaturation/aggregation of b-lactoglobulin (β-lg) is dominantly responsible for the... more Heat-induced denaturation/aggregation of b-lactoglobulin (β-lg) is dominantly responsible for the functional properties of whey. The nature of the aggregates obtained (size, shape, type of interactions between proteins within the aggregates, etc.) strongly affects protein functionalities. It has been shown that proteins within the aggregates are maintained through covalent bonds (disulfide bonds) and/or non-covalent interactions; intermolecular disulfide bonds being prevalent at neutral pH [1, 2]. These covalent bonds result either from sulfhydryl/disulfide exchange reaction, that promotes the propagation of intermolecular exchange reactions through the release of another sulfhydryl group or by sulfhydryl oxidation that behaves as a termination reaction due to the simultaneous disappearance of 2 sulfhydryl groups [3]. In this study we have investigated the influence of small amounts of CuCl2 on the heatdenaturation/aggregation of β-lg A & B at neutral pH. The molecular species resul...
Whey proteins are used for their functional properties in many food applications. The occurrence ... more Whey proteins are used for their functional properties in many food applications. The occurrence of non-native molecular structures during preparation or storage of whey protein ingredients is often responsible for variations in whey protein performances/reproducibility. This occurs since the process of denaturation/aggregation of whey proteins under the conditions used in the above operations is not controlled. However, some non-native molecular structures were shown to have interesting new functional properties, for instance interfacial properties (foaming, emulsifying). In order to develop such improved functionalities, whey proteins are usually destabilized/denatured/aggregated but should be still soluble. Heat treatment of whey proteins in conditions that delay aggregation versus denaturation may be used (extreme pH, low ionic strength, presence of Ca2+-scavengers or caseins, etc.). Another possibility comes from an interruption of the propagation of the aggregation process of ...
Dairy Science & Technology, 2014
The native whey proteins have been intensively used in a multitude of food applications due to th... more The native whey proteins have been intensively used in a multitude of food applications due to their high nutritional, biological, and versatile technofunctional properties. The range of applications of whey proteins has further been extended in the last decades by the use of whey protein aggregates offering new technofunctional properties. These properties are directly dependent on the structure of whey protein aggregates, i.e., their size, shape, density, surface properties, and the type of bonds maintaining proteins together in the aggregates. In this review, after a brief description of the major whey proteins, we examine the most important advances reported to date pertaining to the available approaches to modify the structure of whey proteins for specific functionalities. Our laboratory, Science and Technology of Milk and Eggs, has contributed significantly to the advancement of knowledge on the structure-function relationships of whey proteins either in the native or denatured/aggregated forms. Our expertise and research approaches are highlighted throughout some selected results accumulated during the last decade in comparison with results from the literature.
Journal of Animal and Plant Sciences
Functional foods containing probiotic bacteria (lactic acid bacteria and bifidobacteria) are gett... more Functional foods containing probiotic bacteria (lactic acid bacteria and bifidobacteria) are getting popularity in the world, due to tremendous health benefits conferred by these bacteria. However, the total viable count of bacteria in the final product and the sensory attributes of the product are of higher importance for its consumer acceptability. In this study, flavored (strawberry, pineapple, and mango) probiotic acidophilus milk (from buffalo) using probiotic starter culture (Lactobacillus acidophilus) was prepared and its microbiological, physicochemical and sensory quality studies were carried out up to 6 days of storage. A slight increase in acidity of the milk was observed after 6 days of storage resulting in a decrease of pH (from pH 4.5 to 4.3). Total viable count of L. acidophilus bacteria was decreased after 6 days of storage due to increase in acidity but it was still within acceptable range (>10 6). Sensory evaluation data shows that the quality of sensory attribu...
In the present work, we investigated the structural modifications occurring during the dry heatin... more In the present work, we investigated the structural modifications occurring during the dry heating of model whey proteins, β-lactoglobulin and α-lactalbumin. Samples were adjusted to pH 6.5, water activity a w = 0.23 and dry heated at 100°C for up to 24 h, and the structural modifications followed by gel permeation chromatography, reverse phase-HPLC, SDS PAGE and mass spectrometry (LC-MS/MS). The dry heating treatment traps a fraction of the proteins into covalently linked soluble aggregates. Moreover, a high proportion of non-aggregated α-lactalbumin (about 73%) was converted into non-native forms. The characteristic of those non-native species was the loss of one or two water molecules per α-lactalbumin molecules. Using tandem mass spectrometric peptide mapping, these chemical modifications were found to be attributed to (i) the formation of a pyroglutamic acid from the N-terminal glutamic acid and (ii) the formation of an internal cyclic imide at position Asp 64 . The non-native species were not favored in the case of β-lactoglobulin as they represented less than 18% of non-aggregated proteins.
Journal of Food Engineering, Jan 1, 2012
Procedia Food Science, Jan 1, 2011
Food Chemistry, Jan 1, 2011
Food Chemistry, Jan 1, 2009
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Papers by Muhammad Gulzar