Muhammad Ammar Khan

Thermosonication as a potential quality enhancement technique of apple juice.

Enzymatic browning and microbial growth lead to quality losses in apple products. In the present study, fresh apple juice was thermosonicated using ultrasound in-bath (25 kHz, 30 min, 0.06 W cm(-3)) and ultrasound with-probe sonicator (20 kHz, 5 and 10 min, 0.30 W cm(-3)) at 20, 40 and 60°C for inactivation of enzymes (polyphenolase, peroxidase and pectinmethylesterase) and microflora (total plate count, yeast and mold). Additionally, ascorbic acid, total phenolics, flavonoids, flavonols, pH, titratable acidity, (°)Brix and color values influenced by thermosonication were investigated. The highest inactivation of enzymes was obtained in ultrasound with-probe at 60°C for 10 min, and the microbial population was completely inactivated at 60°C. The retention of ascorbic acid, total phenolics, flavonoids and flavonols were significantly higher in ultrasound with-probe than ultrasound in-bath at 60°C. These results indicated the usefulness of thermosonication for apple juice processing at low temperature, for enhanced inactivation of enzymes and microorganisms.

Effect of multiple freeze-thaw cycles on the quality of chicken breast meat.

The objective of this study was to determine the effects of repeated freeze-thaw cycles (0-6) on any physico-chemical changes and lipid and protein oxidation in chicken breast. The results showed that meat colour, a(∗) (redness) and b(∗) (yellowness) values decreased while L(∗) values (lightness) increased with increasing cycle numbers. Increasing freeze-thaw cycles resulted in a greater degree of lipid and protein oxidation, as evidenced by higher contents of malondialdehyde and carbonyl compounds, and lower contents of sulfhydryl groups. Differential scanning calorimetry profiles and SDS-PAGE banding patterns of myofibrillar proteins indicated slight denaturation of myosin and actin with repeated freeze-thaw cycles. The structural changes occurring in proteins caused by oxidation directly affected the ability of muscles to retain water, as confirmed by the nuclear magnetic resonance relaxometery profile. In conclusion, multiple freeze-thaw cycles increased lipid and protein oxidation and decreased water holding capacity and colour stability of broiler chicken breast.

Effect of protein structure on water and fat distribution during meat gelling.

Emulsion-type sausages were produced, at 80°C for either 0, 10, 20 or 30min, using homogeneous Taihu pork batters. Low-field nuclear magnetic resonance (LF-NMR), with or without deuterium oxide (D2O) substitution, evaluated the proton mobility states related to both water and fat molecules, or fat molecules only, respectively, in the sausage samples, during heat-induced gelation. The decreasing trend in the area proportion of main peak T21, reflected a tighter gel structure in emulsion-type sausages. Raman spectra (400-3600cm(-1)) revealed decreased α-helix, but increased β-sheet, β-turns and random coil contents, during the gelling process. Moreover, principal component analysis (PCA) showed significant correlations between secondary protein structures with distribution of water and fat in the gel matrix. Furthermore, this study established the relationship of water and fat protons mobility with changes in secondary protein structures, and described the critical time of gel formation in emulsion-type pork sausages.

The effect of dietary supplementation with the natural carotenoids curcumin and lutein on pigmentation, oxidative stability and quality of meat from broiler chickens affected by a coccidiosis challenge.

Abstract 1. An experiment was performed to evaluate the effectiveness of the antioxidants curcumin (CRM) and lutein (LTN) on the quality of meat from coccidiosis-infected broilers. A total of 200 one-day-old Arbor Acre chicks were randomly assigned to a treatment group with 5 replicates. The treatments included a basal diet without carotenoid supplementation (control), with 300 mg/kg CRM, with 300 mg/kg LTN or with a combination (C + L) of 150 mg/kg CRM and 150 mg/kg LTN. All chickens were challenged with Eimeria maxima at 21 d old. 2. The results revealed that the coccidiosis reduced redness of meat, while supplementation with carotenoids improved the fresh meat’s redness (a*) and yellowness (b*) and contributed to colour stability maintenance after storage (1 month at −18°C and 3 d at 4°C). 3. Coccidiosis did not produce lipid and protein oxidation in fresh meat, but after storage for one month, the malondialdehyde levels and carbonyl contents were lower in the CRM and C + L birds and the sulfhydryl contents were higher in C + L birds. 4. The sodium dodecyl sulphate–polyacrylamide gel electrophoresis banding pattern showed equivalent myosin chain fragmentations in all treatment groups, whereas lower intensity actin bands were observed in the control group (CONT). Moreover, myofibril protein denaturation (differential scanning calorimetry) profiles showed a reduction in the CONT myosin and actin peaks. Coccidiosis reduced the meat’s water holding capacity in non-supplemented chicken meat and was improved by natural carotenoid. 5. These results emphasise that coccidiosis did not decrease the eating quality of fresh meat, that natural carotenoids are efficient antioxidants and that CRM (300 mg/kg) fed individually or combined with LTN was the most effective supplemented antioxidant compound.

Changes in protein structures to improve the rheology and texture of reduced-fat sausages using high pressure processing

This study investigated the role of high-pressure processing (HPP) for improving the functional properties of meat batters and the textural properties of reduced-fat sausages. Application of 200MPa pressure at 10°C for 2min to pork batters containing various fat contents (0-30%) affected their rheological properties, cooking losses, color, textual properties and their protein imaging. The results revealed that both application of 200MPa and increasing fat content decreased cooking loss, as well as improved the textural and rheological properties. Cooking losses, texture and sensory evaluation of 200MPa treated sausages having 20% fat were similar to those of the 0.1MPa treated sausages having 30% fat. Principal component analysis revealed that certain quality attributes were affected differently by the levels of fat addition and by HPP. These findings indicated the potential of HPP for improving yield and texture of emulsion-type sausages having reduced fat contents.