Zhuang-Li Kang

Isolation and identification of antioxidant peptides from jinhua ham.

The antioxidant activities of the peptides extracted from Jinhua ham were evaluated on the basis of hydroxyl radical scavenging activity, DPPH radical scavenging activity, and Fe(2+) chelating ability. The peptide extracts exhibited great hydroxyl radical scavenging activity and DPPH radical scavenging activity as well as Fe(2+) chelating ability at the concentration of 1 mg/mL, which suggested the presence of peptides with antioxidant activity. The peptides were separated using size exclusion chromatography and reversed-phase HPLC. The fraction with highest DPPH radical scavenging activity was further purified and identified using liquid chromatography tandem matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (HPLC-MALDI-TOF/TOF-MS). The sequence of the antioxidant peptide was identified as Gly-Lys-Phe-Asn-Val. The assessment of fractions indicated that the hydrophobic fractions contributed more to free radical scavenging activities than the hydrophilic peptides. It was concluded that natural peptides extracted and isolated from the Jinhua ham by several chromatographic techniques have antioxidant activities.

Stability of an antioxidant peptide extracted from Jinhua ham

The effects of NaCl, temperature, pH, light intensity and a simulated gastro-intestinal digestion were assessed to determine the stability of antioxidant peptides extracted from Chinese Jinhua ham. Antioxidant peptides showed good stabilities when NaCl content was less than 6%, temperature was lower than 60 °C and they were not exposed to light directly. However, the antioxidant peptides lost antioxidant activities rapidly under alkaline condition. The results of a simulated two-stage digestion system showed that antioxidant activity increased with pepsin treatment but declined with further hydrolysis with trypsin. Pepsin was effective to hydrolyze peptides into smaller fractions leading to the increased exposure of internal hydrophobic amino acids, but trypsin could hydrolyze peptides into more free amino acids resulting in the decline in surface hydrophobicity which affected antioxidant activity of peptides. These suggest that antioxidant peptides extracted from Jinhua ham could maintain their antioxidant activity under the proper conditions.

Effects of the sugarcane dietary fiber and pre-emulsified sesame oil on low-fat meat batter physicochemical property, texture, and microstructure

The purpose of this study was to evaluate the effects of sugarcane dietary fiber (SDF) and pre-emulsified sesame oil for pork fat replacement on batter characteristics. Replacing pork fat with SDF and pre-emulsified sesame oil significantly affected color, water- and fat-binding properties, texture, dynamic rheology, microstructure and sensory analysis. With SDF and pre-emulsified sesame oil, the batters had improved textures and gave good sensory scores. These batters containing SDF had reduced the cholesterol and fat contents. With increasing levels of SDF, the batters had higher water- and fat-binding properties, improved texture (hardness, gumminess and chewiness), dynamic rheology and a more balanced nutritional composition. However, when the level of SDF reached 3%, the pores formed by SDF in batter were too large to hinder aggregation and the hardness of batter was unacceptable, which result the allover acceptability to be unsatisfactory. The sample 2% SDF had comparable overall acceptability to the control batter.

Effect of Flavourzyme on proteolysis, antioxidant capacity and sensory attributes of Chinese sausage.

The objective of this study was to investigate the effect of Flavourzyme, at levels of 0 (control) 4, 8, 12, 16 and 20 LAPU/kg raw meat, on the proteolysis, antioxidant capacity and sensory attributes of Chinese sausage made at 50 °C for 48 h. Results showed that Flavourzyme addition in Chinese sausage accelerated protein degradation, which was reflected by the increase of non-protein nitrogen and appearance of new protein bands in both water-soluble and salt-soluble proteins. By adding Flavourzyme, texture profile analysis (TPA) parameters decreased significantly, and aroma, taste and texture scores were enhanced, respectively. The best sensory attributes were obtained at 8 and 12 LAPU/kg Flavourzyme dose. Besides, Flavourzyme addition enhanced antioxidant capacity, lowered water activity and TBARS values of Chinese sausage. Therefore, moderate Flavourzyme addition is a novel method with great potential to improve eating properties and storage stability of Chinese sausage.

Effect of beating processing, as a means of reducing salt content in frankfurters: A physico-chemical and Raman spectroscopic study

Structural changes, L(⁎)-value, cooking yield changes and textural properties of pork frankfurters containing 1% or 2% salt, produced by the two methods were studied by Raman spectroscopy and texture profile analysis. Increasing salt content from 1% to 2% increased the L(⁎)-value, cooking yield and hardness, and decreased (p<0.05) the C-H stretching and CH2 and CH3 bending vibrations, but did not affect the changes of secondary structures, tryptophan or tyrosine residues. Compared with the chopping, the beating increased L(⁎)-value, cooking yield and hardness of the frankfurters in both salt concentrations. It also resulted in an increase in β-sheets, accompanied by a significant (p<0.05) decrease in α-helix content, a greater exposure of tyrosine residues to the polar environment and a decrease in the CH stretching and CH2 and CH3 bending vibrations. The results showed that the beating process enabled lowering of the salt content while improving the L(⁎)-value, cooking yield and hardness of the frankfurters.

Effect of a beating process, as a means of reducing salt content in Chinese-style meatballs (kung-wan): a physico-chemical and textural study.

Two different meat-cutting methods were used to prepare kung-wans in an attempt to produce low-salt products while retaining the same, or improved, textural and physicochemical properties of the standard high-salt formulation. The level of salt and the processing method significantly affected color, cooking yield, texture and changes in the secondary structures of proteins. Improved salt levels resulted in firmer texture. At the same salt levels, compared with chopping, the beating method resulted in higher L(*)-values, improved cooking yields and changes in the β-sheet content of the proteins, which resulted in an improved product with better texture. Using the beating process, the kung-wans prepared with 1% and 2% salt had similar L(*)-values, cooking yield and texture, and were better than those prepared by chopping with 2% salt. Overall, the beating process enabled lowering of the salt content, making the kung-wans more hard, brittle and elastic.

Evaluation of protein structural changes and water mobility in chicken liver paste batters prepared with plant oil substituting pork back-fat combined with pre-emulsification.

Protein structural changes and water mobility properties in chicken liver paste batters prepared with plant oil (sunflower and canola oil combinations) substituting 0-40% pork back-fat combined with pre-emulsification were studied by Raman spectroscopy and low-field nuclear magnetic resonance (NMR). Results showed that pre-emulsifying back-fat and plant oil, including substituting higher than 20% back-fat with plant oil increased the water- and fat-binding (p<0.05) properties, formed more even and fine microstructures, and gradually decreased the NMR relaxation times (T21a, T21b and T22), which was related to the lower fluid losses in chicken liver paste batters. Raman spectroscopy revealed that compared with a control, there was a decrease (p<0.05) in α-helix content accompanied by an increase (p<0.05) in β-sheet structure when substituting 20-40% back-fat with plant oil combined with pre-emulsification. Pre-emulsification and plant oil substitution changed tryptophan and tyrosine doublet hydrophobic residues in chicken liver paste batters.

Combination of κ-Carrageenan and Soy Protein Isolate Effects on Functional Properties of Chopped Low-Fat Pork Batters During Heat-Induced Gelation

The current study was conducted to investigate combination impacts of κ-carrageenan (CAR) and soy protein isolate (SPI) on the functional properties of chopped low-fat pork batters during heat-induced gelation. Texture profile analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Raman spectroscopy, and scanning electron microscopy (SEM) were used to determine the properties of pork batters. The addition of individual CAR and SPI or CAR/SPI mixture improved textural properties except for cohesiveness compared with the control (P < 0.05). The cooking loss with supplemented ingredients was significantly lowered, while the thermal emulsion stability was improved compared to that of the control (P < 0.05). Compared with the control, the CAR/SPI mixture formed a more continuous structure evidenced by more uniform fat particles and a more compact protein matrix. Raman spectroscopy showed that pork batters with ingredients resulted in a lower content of α-helice and a higher content of β-sheet, β-turn, and random coil compared with the control. However, no interactions between meat protein and CAR/SPI could be identified by SDS-PAGE profiles. The results indicate that the combination of CAR/SPI can be effectively used to improve functional properties of low-fat pork batters effectively.

Effect of a beating process, as a means of reducing salt content in Chinese-style meatballs (kung-wan): a dynamic rheological and Raman spectroscopy study.

Chopping and beating processes were used as meat-cutting methods in preparing kung-wan to produce low-salt products while retaining or improving the emulsion stability, sensory evaluation, and physico-chemical properties of the standard high-salt formulation. Increased salt content improved emulsion stability and dynamic rheology. However, 3% salt content decreased the overall acceptance of kung-wan. Compared with the chopping process, beating resulted in higher emulsion stability, overall acceptance, and β-sheet content (P<0.05). Additionally, the beating process formed more compact and continuous structures at the same salt content. Kung-wan produced by beating with 1% and 2% salt had similar emulsion stabilities, sensory evaluation, and secondary structures (P>0.05). Therefore, this process allows reduction of salt content, suggesting that the kung-wan produced in this manner is healthier and has better texture.

Reduced functionality of PSE-like chicken breast meat batter resulting from alterations in protein conformation

The objectives of this study were to evaluate protein thermal stability, water-protein interaction, microstructure, and protein conformation between PSE-like and normal chicken breast meat batters. Sixty pale, soft, and exudative (PSE)-like (L*>53, pH24 h<5.7) and 60 normal (46<L*<53, 5.7<pH24 h<6.1) chicken breast meats were selected from 3 different occasions in a major Chinese commercial plant. Two different meat batters were formulated to 14% meat protein and 2% salt, and they were analyzed for the protein changes and the microstructure using differential scanning calorimetry, low-field (LF)-NMR, SEM, and Raman spectroscopy. PSE-like meat batter had lower gel strength, water-holding capacity, and salt-soluble protein extraction (P<0.05). Heated PSE-like meat batter formed an aggregated gel matrix, while normal meat batter produced a compact gel network with fine, cross-linked strands by many protein filaments. LF-NMR revealed an increase in the water mobility in heated PSE-like meat batter with an increasing amount of loosely bound water (P<0.05). No significant changes were observed in the electrophoretic patterns of salt-soluble protein extracts by SDS-PAGE. However, differential scanning calorimetry showed that PSE-like meat had greater myosin and sarcoplasmic proteins/collagen denaturation (P<0.05). In PSE-like meat, actin denaturation was particular evident after salt addition (P<0.05) using differential scanning calorimetry. Moreover, Raman spectroscopy indicated that PSE-like meat batter had less unfolded α-helix and β-sheet structure formation, reduced exposure of hydrophobic and tyrosine residues (P<0.05), and changes in the microenvironment of aliphatic residues and tryptophan, which affected salt-soluble protein extraction, gel properties, and water-holding capacity. In conclusion, the inferior functional properties of PSE-like meat were attributed to not only myosin denaturation, but also actin denaturation after salt addition and different protein structural states.