Effect of Processing Conditions on the Bioavailability and Nutritional Quality of Pork Proteins

Research output: Book/ReportPh.D. thesisResearch

  • Bhaskar Mitra
The vision of the project was to portray the impact of time temperature combinations on the structural elucidation, chemical modification, proteomics evaluation for residue level changes which could in turn affect digestibility and meat quality. With raw as control (RAW), assorted heat treatments involved were 58 (SV5872), 80 (SV8072), 98 (B9872) and 160 °C (OV16072) for 72 min, 118 °C for 8 min (AC1188) and 58 °C for 17 h (SV5817), resembling most common processing procedures. Structural modifications of pork proteins were studied. Protein denaturation, surface protein hydrophobicity state and protein aggregation behaviour were investigated. Modifications and molecular chemistry in protein structures were tracked by Fourier Transform Infrared Spectroscopy in order to extract relative proportions of secondary structures and residual conformations. Differential scanning calorimetry showed endothermic transitions indicating different regions of protein denaturation with respect to increase in temperature range. Our observation in this study was that temperature and too some extent time do influence structural changes and this in turn might accelerate or decrease protein degradation. Effect of temperature-time profiles were investigated on oxidation markers like α-Aminoadipic and γ-Glutamic semialdehydes, extent of tryptophan degradation and formation of fluorescent oxidation products. Free thiol content was also analysed to track cysteine oxidation. With heating, partial and full unfolding of protein structure was observed which indicated exposure of hydrophobic amino acid domains and their subsequent reaction with regard to oxidation. Accumulation of fluorescent oxidation products was observed with high temperature and longer time. Semialdehyde formation increased in the beginning but was constant at higher temperatures possibly because they participated in other side reactions. Through redox proteomics, peptide modifications like oxidation, protein carbonyls, lipid oxidation products and hydroxykynurenin (tryptophan oxidation products) were detected at residue level. Conclusion derived is oxidation might impair functionality and nutritional quality of proteins. Heating encourages formation of first stage and late stage Maillard reaction compounds. Furosine, being an important marker for heat treatment index, was detected in all groups with roasting having a 4-fold increase over the raw samples. Slightly harsh treatment methods like boiling and autoclaving did contribute to a significant increase in furosine. Nɛ-carboxymethyllysine (CML), being a crucial indicator for AGEs, were analyzed by mass spectrometry with raw samples having negligible amount but with temperature rise they too increased. A similar increasing trend could be observed in Lanthionine (LAN), covalently bonded protein crosslinks, which arise due to severe thermal regimes. Simultaneously, glycation and deamidation formation were tracked in meat fractions through peptidomics to highlight residue level changes that might affect nutrient value in processed muscle based foods.
Digestibility rates were determined via in vitro models in gastric and intestinal phase. Samples were then subjected to pepsin at pH 3.00 in the gastric phase followed by trypsin and α-chymotrypsin at pH 8.00 in the intestinal phase. With reference to stomach conditions, gastric values indicated that samples cooked at low temperature had a significantly higher proteolytic activity than ones treated at higher temperature. No major or significant change could be detected in the duodenal phase but for intestinal proteolytic rate at end time point, low temperature group had a slight significant and higher difference than the roasted samples. Partial least squares model generated also gave us an in-depth idea about an inverse relationship that existe
Original languageEnglish
PublisherDepartment of Food Science, Faculty of Science, University of Copenhagen
Publication statusPublished - 2018

ID: 200971025