Relevance of collagen solubility and gelatinolytic proteinase activity for texture softening in chilled grass carp (Ctenopharyngodon idellus) fillets

The aim of the present study was to investigate the underlying mechanisms of softening texture in chilled grass carp filletsunderpinning collagen solubility, gelatinolytic proteinase activity and physicochemical parameters. Acid-soluble collagen (ASC) and heat soluble collagen (HSC) increased markedly, while a significant decline was detected in total collagen and insoluble collagen (ISC) during the first 3 days of storage, coinciding with a loss of shear force and water-holding capacity (WHC) (P < 0.05). Moreover, the activity of gelatinolytic proteinases was gradually activated and reached the peak at day 3 (P < 0.05). Pearson coefficient analysis showed that gelatinolytic proteinase activity revealed a significant correlation with collagen solubility. Total collagen, ASC, ISC and HSC were significantly correlated with shear force and WHC. Our study clarified that the increase of collagen solubility by gelatinolytic proteinases played an important role for texture softening in the early stage of chilled grass carp fillets.     

The impact of collagen on softening of grass carp (Ctenopharyngodon idella) fillets stored under superchilled and ice storage

The objective of this work was to study the impact of collagen on softening of grass carp (Ctenopharyngodon idella) fillets during chilled storage. The fillets were stored under superchilling (?1.5 ± 0.2 °C) and with ice (0.2 ± 0.1 °C) for 21 days, and texture properties, collagen and the related enzyme activities were measured. Results showed that firmness and collagen content were strongly influenced by storage temperature and time. Fillet firmness decreased by 32.3% (superchilling) and 49.6% (ice stored) of the initial values after 3 days of storage, respectively. Total collagen content decreased with time, but different collagen fractions showed variations. Collagen degraded to different extents depending on storage conditions as indicated by SDS‐PAGE and amino acid analysis. In addition, collagenase activity declined significantly during the first 3 days, followed by a slow increase. This study demonstrated that collagen degradation was involved in grass carp fillet softening and provided useful information for fillet quality improvement.     

Broad‐spectrum inhibition of proteolytic enzymes by allicin and application in mitigating textural deterioration of ice‐stored grass carp (Ctenopharyngodon idella) fillets

The inhibitory effect of allicin on proteolytic enzymes and textural deterioration of ice‐stored grass carp (Ctenopharyngodon idella) fillets was investigated. The results of in vitro study showed that allicin inhibited the activity of cathepsin B, L and D, calpain and collagenase in crude extract of grass carp muscle. Among endogenous enzymes, cathepsin B, L and collagenase were the most susceptible to allicin. Proteolysis of myofibrillar proteins by either crude enzyme or cathepsin B and L was almost prevented by allicin when employed at a concentration higher than 100 mm . After storage of 21 days, shear force of fillets treated with allicin at 10–100 mm was 39–51% higher than that of control. Myofibrillar proteins of fillets during storage were well protected against degradation when allicin concentration increased to 100 mm , as evidenced by SDS‐PAGE. Therefore, allicin could be a potential broad‐spectrum inhibitor to retard softening of fish fillets via mitigating myofibrillar proteolysis by endogenous enzymes especially cathepsin B and L during ice‐storage.     

High‐pressure processing‐induced conformational changes during heating affect water holding capacity of myosin gel

This study aimed to investigate the effects of high‐pressure processing (HPP) (0.1‐400 MPa for 9 min) on the water holding capacity (WHC) of heat‐induced rabbit myosin gel and structural changes during thermal treatment (25–75 °C). HPP at 100 MPa significantly increased the WHC (P < 0.05) and formed more regular and homogeneous three‐dimensional network. Myosin tails at 100 MPa unfolded completely during the thermal treatment, which was beneficial to form a high WHC gel network. However, myosin pressurised at 200 MPa and above formed a weak gel. Their heads were already aggregated before heating, preventing from subsequent thermal denaturation and aggregation. With the temperature increasing, unfolding of myosin tails was not sufficient for a filamentous network formation. These results suggested that HPP could modify the myosin structure and affect the gel formation during heating. The 100 MPa was the optimum pressure level for the WHC of rabbit myosin gel.     

Effect of plant polyphenols and ascorbic acid on lipid oxidation,residual nitrite and N‐nitrosamines formation in dry‐cured sausage

The effects of green tea,grape seed polyphenols and ascorbic acid on pH, water activity (a_w), microbiological counts, TBARS, residual nitrite and N‐nitrosamines were determined in dry‐cured sausages during the ripening period. Results showed that TBARS increased gradually during ripening (P < 0.05), but were significantly reduced with plant polyphenols and ascorbic acid (P < 0.05). Green tea polyphenol (GTP) was most effective (P < 0.05) in reducing TBARS. Plant polyphenols and ascorbic acid significantly decreased residual nitrite, ascorbic acid being most effective (P < 0.05). The amount of N‐nitrosamines increased during ripening, but was significantly reduced with plant polyphenols and ascorbic acid (P < 0.05). Plant polyphenols had no significant effects on moisture content, a_w, pH or microbiological counts in dry‐cured sausage during ripening (P > 0.05). It was concluded that plant polyphenols and ascorbic acid were effective in maintaining the quality and safety of dry‐cured sausages.     

Grass carp peptides hydrolysed by the combination of Alcalase and Neutrase: Angiotensin‐I converting enzyme (ACE) inhibitory activity,antioxidant activities and physicochemical profiles

In this study, grass carp peptides were prepared by enzymatic hydrolysis of grass carp protein using the combination of Alcalase and Neutrase, and angiotensin‐I converting enzyme (ACE) inhibitory activity in vitro, antihypertensive activity in vivo, antioxidant activities, and physicochemical properties of peptides achieved from grass carp protein were characterised after ultrafiltration and desalted processes using mixed ion exchange resins. The purified peptides exhibited strong ACE inhibitory activity (IC₅₀ = 105 μg mL^?1), antihypertensive activity with the maximal drop for systolic blood pressure (SBP) of 43 mmHg at a dosage of 100 mg per kg body weight in spontaneously hypertensive rat (SHR), and antioxidant activities indicated by thiobarbituric acid‐reactive substance values in a liposome‐oxidising system, radical‐scavenging activity and chelation of metal ions (Fe²⁺). The molecular weight of peptides was <1000 Da. Compared to grass carp protein, the peptides separated from enzymatic hydrolysates possessed similar amino acid compositions, but contained higher concentrations of essential amino acids. Moreover, the peptides exhibited excellent solubility at a wide range of pH values from 2 to 10, and lower apparent viscosity than the protein. The peptides separated from enzymatic hydrolysates might be used as a promising ingredient in antihypertensive functional foods and nutraceuticals.     

The function of endogenous cathepsin in quality deterioration of grass carp (Ctenopharyngodon idella) fillets stored in chilling conditions

Changes of textural properties and cathepsin activity of grass carp fillets during storage in superchilling (?1.5 ± 0.2 °C) and ice (0.2 ± 0.1 °C) was investigated, and the function of cathepsin in quality deterioration of grass carp fillets was discussed. Results showed that shear force of superchilled and ice‐stored fillets decreased by 50% and 55% after 6 days of storage, respectively. The cathepsin activies in different fractions changed significantly during storage at both conditions. Cathepsin B, B+L activities in sarcoplasma, myofibrillar and heavy mitochondrial fraction significantly increased during the early 3 days postmortem, accompanied by remarkable reduction of corresponding activity in lysosome. Cathepsin D activity in sarcoplasma and myofibrillar significantly increased during 6 days of storage with corresponding decrease in lysosome and heavy mitochondria. Correlation analysis showed that changes of shear force of grass carp fillets were significantly correlated with integration of cathepsin B, D and B+L throughout storage time (r² > 0.94). As derived from the first‐order exponential decay model, the enzyme efficiencies (k_a) of cathepsin B and B+L were more than twofold higher than those of cathepsin D, suggesting the major role of cathepsin B and B+L in textural deterioration of grass carp fillets in chilling storage.     

Effect of total milk solid content adjusted by adding ultrafiltered milk retentate on quality of set mango yoghurt

The quality of set mango yoghurt prepared by varying total milk solids (TMS) level in mango yoghurt mix, by adding 5× ultrafiltered cow skim milk retentate and cow milk cream, was investigated. The water‐holding capacity (WHC) and values of textural attributes of mango yoghurt increased, whereas body and texture and overall acceptability scores decreased significantly (P < 0.05) with increasing TMS level. The optimised product (10.2% TMS level) was compared with conventional mango yoghurt. Acetaldehyde concentration, WHC, values of textural attributes, body and texture, overall acceptability scores and pH were significantly (P < 0.05) higher in optimised compared with conventional mango yoghurt.     

Influence of rapid chilling on biochemical parameters governing the water‐holding capacity of pork longissimus dorsi

The aim of this study was to investigate the effects of rapid chilling (RC) of carcasses on the quality of pork longissimus dorsi (LD) compared to conventional chilling (CC). Carcasses subjected to RC were chilled at ?20 °C for 1.5 h and then moved to 4 °C until 24 h post‐mortem, while carcasses that were CC were placed directly in a chill at 4 °C for 24 h post‐mortem. RC accelerated the rates of temperature decline post‐mortem (P < 0.01) and increased pH values at 1.5 and 8 h post‐mortem (P < 0.05). RC could significantly decrease the denaturation of myosin and sarcoplasmic proteins during post‐mortem ageing. Samples of RC had a significant lower purge loss compared to CC group during post‐mortem ageing (P < 0.05). Our study implies that RC could influence the biochemical changes of pork LD which may further regulate water‐holding capacity during post‐mortem ageing.     

Effects of different prebiotic stabilisers and types of molasses on physicochemical,sensory, colour and mineral characteristics of probiotic set yoghurt

The physicochemical, sensory, properties and mineral profile of probiotic set yoghurts prepared with different prebiotic stabilisers (pectin and guar) at 0.5% (w/v) and different molasses (grape, mulberry and carob) at 10% (v/v) were investigated. Guar‐supplemented yoghurts had the lowest titratable acidity values (P < 0.01) also the highest water‐holding capacity values (P < 0.01). However, guar had a negative effect on gel firmness and sensory properties of yoghurts. The effect of different stabilisers and molasses on colour L* and a*values was statistically significant (P < 0.01). Panelists gave the highest flavour scores to the pectin‐added yoghurts during storage period (P < 0.01).     

The "sponge effect" hypothesis: an alternative explanation of the improvement in the waterholding capacity of meat with ageing

Bovine M. semimembranosus from different sexes of cattle were held at temperatures ranging from 0 to 35 °C until rigor and aged for up to 9 weeks. The waterholding capacity (WHC) of the beef increased with ageing as evidenced by the decline in drip loss measured gravimetrically, centrifugally and by pressure. Drip viscosity (P < 0.01), meat protein extractability (P < 0.05), spreadability (P < 0.01) and compressibility also increased with ageing. Evidence of structural changes was seen in SDS-PAGE confirming the physical changes. Meat spreadability under pressure and WHC were higher in samples with inherently higher pH relative to lower pH. The outcome of this study supports a hypothesis that the increase in WHC with ageing is due to the breakdown in meat structure and the creation of “sponge effect”, which disrupts the channels through which moisture is lost and physically entraps the free water in meat and reduce the amount that drips out.     

Effect of salt content on gelation of normal and wooden breast myopathy chicken pectoralis major meat batters

This study investigated the effects of salt content (0–4%) on water holding capacity (WHC), textural characteristics, rheological properties, and microstructure of cooked normal (NOR) and wooden breast (WB) chicken meat batters. Results indicated with 0–2% salt addition, the WB batters had significantly lower WHC and storage modulus (G’) compared with the NORs (P < 0.05). However, these differences were eliminated when salt contents were increased to 3% or 4%. In addition, the NORs formed more regular and pored networks than the WBs (0–2%). Salt level significantly affected the textural properties of both batter types (P < 0.05). The hardness of the WB batters was lower than NORs at all NaCl levels (P < 0.05). Overall, compared with NORs, the WB batters showed inferior gelation properties at salt contents of 0–2%, while increasing salt content to 3–4% can improve the WHC and microstructure of gels.     

Preparation and evaluation of low‐calorie functional ice cream containing inulin,lactulose and Bifidobacterium lactis

This study was aimed to investigate the effects of replacing 5% fat and sugar by inulin and lactulose, respectively, on the survival of Bifidobacterium lactis and physicochemical and sensorial characteristics of the ice cream. Total solids, pH, melting rate and sensory scores of low‐fat and/or low‐sugar ice cream samples did not differ significantly from the control. Overrun and hardness of low‐fat samples were significantly higher than that of the control group (P < 0.01). The viable counts of B. lactis in the low‐sugar synbiotic ice creams were significantly lower than that of other groups at the end of 90‐day storage (P < 0.01).     

Inhibition of frozen storage‐induced oxidation and structural changes in myofibril of common carp (Cyprinus carpio) surimi by cryoprotectant and hydrolysed whey protein addition

The objective of the present study was to evaluate the efficacy of combined cryoprotectants (sucrose + sorbitol) and whey protein isolate (WPI) hydrolysates to inhibit protein oxidation and quality loss in common carp (Cyprinus carpio) surimi during frozen storage at ?25 °C. With increasing storage time, the carbonyl content of myofibrillar proteins increased from 4.02 nmolmg^‐1 protein (0 day) to 7.25, 6.31, 5.26 and 4.83 nmol mg^?1 protein (180 days; P < 0.05) for the control and samples with cryoprotectants, with cryoprotectants + WPI hydrolysates and with cryoprotectants + propyl gallate, respectively; protein surface hydrophobicity and turbidity increased in a similar trend, while sulfhydryl content, Ca‐ATPase activity, protein solubility and protein thermal stability decreased (P < 0.05). These results suggest that treatments with combined cryoprotectants and antioxidative WPI hydrolysates offer an effective approach to reducing the extent of protein oxidation in common carp surimi, thereby limiting protein structural changes known to impair texture of surimi products.     

Modelling the cross‐contamination of Listeria monocytogenes in pork during bowl chopping

This study has developed a predictive model for the cross‐contamination of pork by Listeria monocytogenes during bowl chopping. The transfer rates of L. monocytogenes were measured in sixteen chopping scenarios based on practical work. Meanwhile, contaminated bowl chopper was cleaned with either a dry rag (DR), warm water (WW) or 70% ethanol + water (EW), respectively. It was showed that significant differences (P < 0.05) were observed among the three cleaning methods on the reduction of L. monocytogenes, the greatest log reduction being achieved by EW. Moreover, the model introduced by a previous study, predicting cross‐contamination of L. monocytogenes during meat slicing, was improved and validated in this study. Verification results showed that the improved model was acceptable for predicting L. monocytogenes cross‐contamination during pork chopping with coefficients of determination (R² > 0.82), accuracy factors (A_f < 1.44), bias factors (B_f < 1.42), and root mean square error (RMSE < 0.99). Furthermore, the modified model might provide an effective tool for assessing the risk of the cross‐contamination of meat products.     

The effect of traditional production methods on microbial,physico‐chemical and sensory properties of ‘Slovenská bryndza’ Protected Geographical Indication cheese

Bryndza is a natural, white, mature and spreadable kind of cheese, and since 2008, it has been manufactured in specified mountainous areas of the Slovak Republic with Protected Geographical Indication. The aim of this work was to provide useful information about the microbial, physico‐chemical and sensory characteristics of bryndza, taking into consideration the variabilities related to the traditional methods of production technology of three bryndza cheese varieties. Statistically significant differences were observed in bryndza cheese production methods in chemical parameters of NaCl and malondialdehyde content (P < 0.05) and in the microbial presence of Enterococcus spp. (P < 0.001) and Staphylococcus spp. (P < 0.01).     

Acid‐soluble and pepsin‐soluble collagens from grass carp (Ctenopharyngodon idella) skin: a comparative study on physicochemical properties

In this study, acid‐soluble (ASC) and pepsin‐soluble (PSC) collagens with triple helical structures were successfully extracted from the skin of grass carp (Ctenopharyngodon idella) by two different extraction approaches. SDS‐PAGE pattern revealed that ASC and PSC are type I collagens with typical α1, α2 and β‐chains. In addition, the intensity of χ‐chain (trimer) in ASC was higher than that of PSC, representing the presence of the high proportion of intra‐ and intermolecular cross‐links of extracted collagens with large molecular weight using the acid method. Differential scanning calorimetry (DSC) results demonstrate that T_d (69.04 °C) of ASC was higher than T_d (62.20 °C) of PSC. Both ASC and PSC had the highest solubility at acidic pHs or at a low concentration of NaCl (<2%, w/v). The results of FTIR suggested the ASC and PSC maintained in the helical secondary structure at high degree.     

Chicken breast quality – normal,pale, soft and exudative (PSE) and woody – influences the functional properties of meat batters

Three classes (normal, PSE‐like and woody, thirty for per class) of fresh chicken breast meats were selected from a Chinese processing plant. Then, three classes of chicken breast meats were used to prepare meat batters and meatballs. This study investigated the effects of three classes of chicken breast meat on the physicochemical properties, water distribution, protein secondary structures and microstructures of meatballs. PSE‐like and woody meatballs both had lower water holding capacity and textural properties than normal meatballs. Furthermore, the free water mobility and proportion in PSE‐like and woody meatballs were increased (P < 0.05). According to near‐infrared spectroscopy results, the intensity of the 1940‐nm bands of PSE‐like and woody classes both increased. Both PSE‐like and woody meatballs formed more aggregated gel matrices than normal class. PSE‐like and woody classes had higher α‐helix and lower β‐structure contents (P < 0.05). Overall, compared with normal meatballs, PSE‐like and woody meatballs showed inferior functional properties.     

Changes in browning‐related components of apple slices during different stages of instant controlled pressure drop‐assisted hot air drying (AD‐DIC)

The effect of instant controlled pressure drop‐assisted hot air drying (AD‐DIC) on browning‐related components in apple slices was studied. Results showed the AD temperature had no significant effect on colour index of final apple slices. The aspartic acid, glutamic acid, lysine, histidine, arginine, sucrose and dehydroascorbic acid (DHAA) in apple slices increased firstly during the AD process and then decreased during DIC process. The fructose, glucose, reduced ascorbic acid and major phenolic compounds reduced with the abrupt increase of 5‐hydroxymethylfurfural (5‐HMF) during AD‐DIC. There were significant correlations (P < 0.05) among moisture content (w.b.), water activity (a_w), water state, reduced ascorbic acid, DHAA, chlorogenic acid, procyanidin B₁, (+)‐catechin, (?)‐epicatechin and phlorizin during AD‐DIC. The colour difference showed that the major browning reaction of apple slices during the predrying process was enzymatic browning, while nonenzymatic browning played a crucial role on green‐red value (CIE a* value) during DIC.