Changes to insulin sensitivity in glucose clearance systems and redox following dietary supplementation with a novel cysteine-rich protein: A pilot randomized controlled trial in humans with type-2 diabetes.

We recently developed a novel keratin-derived protein (KDP) rich in cysteine, glycine, and arginine, with the potential to alter tissue redox status and insulin sensitivity. The KDP was tested in 35 human adults with type-2 diabetes mellitus (T2DM) in a 14-wk randomised controlled pilot trial comprising three 2×20 g supplemental protein/day arms: KDP-whey (KDPWHE), whey (WHEY), non-protein isocaloric control (CON), with standardised exercise. Outcomes were measured morning fasted and following insulin-stimulation (80 mU/m2/min hyperinsulinaemic-isoglycaemic clamp). With KDPWHE supplementation there was good and very-good evidence for moderate-sized increases in insulin-stimulated glucose clearance rate (GCR; 26%; 90% confidence limits, CL 2%, 49%) and skeletal-muscle microvascular blood flow (46%; 16%, 83%), respectively, and good evidence for increased insulin-stimulated sarcoplasmic GLUT4 translocation (18%; 0%, 39%) vs CON. In contrast, WHEY did not effect GCR (-2%; -25%, 21%) and attenuated HbA1c lowering (14%; 5%, 24%) vs CON. KDPWHE effects on basal glutathione in erythrocytes and skeletal muscle were unclear, but in muscle there was very-good evidence for large increases in oxidised peroxiredoxin isoform 2 (oxiPRX2) (19%; 2.2%, 35%) and good evidence for lower GPx1 concentrations (-40%; -4.3%, -63%) vs CON; insulin stimulation, however, attenuated the basal oxiPRX2 response (4%; -16%, 24%), and increased GPx1 (39%; -5%, 101%) and SOD1 (26%; -3%, 60%) protein expression. Effects of KDPWHE on oxiPRX3 and NRF2 content, phosphorylation of capillary eNOS and insulin-signalling proteins upstream of GLUT4 translocation AktSer437 and AS160Thr642 were inconclusive, but there was good evidence for increased IRSSer312 (41%; 3%, 95%), insulin-stimulated NFκB-DNA binding (46%; 3.4%, 105%), and basal PAK-1Thr423/2Thr402 phosphorylation (143%; 66%, 257%) vs WHEY. Our findings provide good evidence to suggest that dietary supplementation with a novel edible keratin protein in humans with T2DM may increase glucose clearance and modify skeletal-muscle tissue redox and insulin sensitivity within systems involving peroxiredoxins, antioxidant expression, and glucose uptake.

Systematic review of emerging and innovative technologies for meat tenderisation.

Consumers are the final step in the meat supply chain and meeting consumer expectations of quality and tenderness are important for satisfaction and repeat purchase. High pressure processing, shockwaves, ultrasound, pulsed electric field and muscle stretching can be applied to pre- and post-rigor meat for tenderisation. These non-thermal and thermal innovative technologies can be used with varying levels of success to cause physical disruption to muscle structure, enhanced proteolysis and ageing and muscle protein denaturation and solubilisation resulting in changes to texture and juiciness. Results of a meta-analysis are used to compare the effects of these technologies on meat tenderisation. In the future, a combination of new and innovative technologies will be ideally suited to deliver a range of desired textures for meat products.

Halal and kosher slaughter methods and meat quality: a review.

There are many slaughter procedures that religions and cultures use around the world. The two that are commercially relevant are the halal and kosher methods practiced by Muslims and Jews respectively. The global trade in red meat and poultry produced using these two methods is substantial, thus the importance of the quality of the meat produced using the methods. Halal and kosher slaughter per se should not affect meat quality more than their industrial equivalents, however, some of their associated pre- and post-slaughter processes do. For instance, the slow decline in blood pressure following a halal pre-slaughter head-only stun and neck cut causes blood splash (ecchymosis) in a range of muscles and organs of slaughtered livestock. Other quality concerns include bruising, hemorrhages, skin discoloration and broken bones particularly in poultry. In addition to these conventional quality issues, the "spiritual quality" of the meat can also be affected when the halal and kosher religious requirements are not fully met during the slaughter process. The nature, causes, importance and mitigations of these and other quality issues related to halal and kosher slaughtering and meat production using these methods are the subjects of this review.

Evaluation of pre-rigor injection of beef with proteases on cooked meat volatile profile after 1 day and 21 days post-mortem storage.

This research was carried out to determine the effects of pre-rigor injection of beef semimembranosus muscle with nine proteases from plant and microbial sources, on the volatile profile of cooked beef after 1 day and 21 days post-mortem (PM) storage using Solid-phase microextraction gas chromatography mass spectrometry analysis. A total of 23 aldehydes, 5 ketones, 3 furans, 8 nitrogen and sulphur compounds, 4 alkanes, 7 alcohols and 6 terpenes were detected. Eleven volatile compounds characteristic of ginger flavour were detected in zingibain-treated meat. Benzaldehyde significantly increased (p<0.05) only in kiwifruit juice (KJ), fungal 31 protease and Asparagus protease (ASP) treated samples from 1 day to 21 days PM storage. A significant increase (p<0.05) in 3-methylbutanal was observed in KJ, bacterial and fungal protease treated samples at 21 days PM storage. Treatments with bromelain, papain, ASP, actinidin, and KJ (except KJ 21 days) proteases resulted in flavour profiles closer to that of the control beef sample.

Pre-rigor infusion with kiwifruit juice improves lamb tenderness.

The ability of pre-rigor infusion of kiwifruit juice to improve the tenderness of lamb was investigated. Lamb carcasses were infused (10% body weight) with fresh kiwifruit juice (Ac), water (W) and a non-infusion control (C) treatment. Infusion treatment had no effect on lamb hot carcass weight, cold carcass weight and chilling evaporative losses. The infused treatment carcasses of Ac and W had lower (P<0.05) pH values than C carcasses during the initial 12h post-mortem. The LD muscles from Ac carcasses were more tender with significantly lower shear force (P<0.001) compared with C and W carcasses during the six days following infusion with the kiwifruit juice. The enhanced proteolytic activity (P=0.002) resulting from the infused kiwifruit juice in Ac carcasses was associated with significant degradation of the myofibrillar proteins, appearance of new peptides and activation of m-calpain during post-mortem ageing. Thus, kiwifruit juice is powerful and easily prepared meat tenderizer, which could contribute efficiently and effectively to the meat tenderization process.

Post-mortem metmyoglobin reduction in fresh venison.

The accumulation of metmyoglobin (MetMb) at the surface of meat during storage contributes significantly to its discolouration. Under appropriate conditions it may be possible to utilise residual meat MetMb reducing activity to maintain fresh colour. Venison meat colour stability is poorer compared with other species. Hence, we evaluated the capacity of completely discoloured venison (n=12 animals) to reduce MetMb under anaerobic conditions in order to decipher more clearly the role MetMb reducing activity may play. The reducing capacity of venison (1 day, 3, and 6 weeks post-mortem), electrical stimulation, surface location (top and bottom) and rigor temperature (15 and 35°C) on MetMb were evaluated. Surface MetMb decreased (P<0.001) during storage while deoxymyoglobin increased (P<0.001) demonstrating MetMb reduction. Metmyoglobin reduction was greater (P<0.001) in venison which entered rigor at 15°C, the reduction at the bottom surface of the steaks was greater (P<0.001) compared with the top surface, and electrical stimulation had no affect (P>0.05). These data demonstrate that metmyoglobin reducing activity occurs anaerobically in completely discoloured venison following storage display. The practical application for this finding needs to be determined.

Effects of rigor temperature and electrical stimulation on venison quality.

The effects of rigor temperature and electrical stimulation on venison quality were assessed using venison longissimus dorsi muscle. In the first trial, effect of rigor temperature (0, 15, 25, 30, 35 and 42°C) and time post-mortem (at rigor, 3, 7 and 14 days) on drip and cooking losses, % expressible water (water holding capacity, WHC), sarcomere length, protein solubility, meat tenderness and colour were investigated. In the second trial, the effects of rigor temperature (15 and 35°C), electric stimulation (stimulated or not stimulated) and time (at rigor, 3 and 6 weeks post-mortem) on tenderness and colour were further investigated. Results of the first trial showed no clearly established trends of the effect of rigor temperature and time on the cooking and drip losses and protein solubility except venison muscles that went into rigor at 42°C tended to have higher drip loss and lower protein solubilities compared to muscles that went into rigor at the other temperatures. Venison water holding capacity (WHC) decreased with the increase in rigor temperature (P<0.001) and venison became more tender with time post-mortem. Venison colour improved with increasing rigor temperature. During display, samples that went into rigor at 15, 25 and 35°C had the lowest and those at 0 and 42°C had the highest rate of change of redness (a(∗)) value with time. In the second trial, tenderness was improved by stimulation (P=0.01). Redness (a(∗)) values were affected by rigor temperature (P<0.01) and post-mortem time (P<0.001) but not by electrical stimulation. It is concluded that venison tenderness can be improved via the manipulation of rigor temperature to obtain acceptable level of tenderness early post-mortem with less damaging effect on colour stability.

Effect of calcium chloride, zinc chloride, and water infusion on metmyoglobin reducing activity and fresh lamb color.

Calcium chloride (CaCl2), zinc chloride (ZnCl2), or water infusions were used to investigate the biochemical factors that affect fresh lamb color, and to examine the role of metmyoglobin-reducing activity in regulating this important quality attribute. Immediately after exsanguination, lamb carcasses (n = 6 per treatment) were infused (10% of BW) with 0.3 M CaCl2, 0.05 M ZnCl2, or water via a catheter inserted into the left carotid artery. The right LM was excised at 24-h postmortem and divided into two halves. The caudal portion was cut into 2.5-cm-thick chops and displayed for 6 d under 1,076 lx of white fluorescent lighting at 2 degrees C, whereas the cranial half was vacuum-packaged and stored at 2 degrees C for 3 wk before retail display. Objective color measurements and samples for biochemical analysis were taken at 0, 1, 3, and 6 d of display. In infused carcasses, pH decline was more rapid (P < 0.05) than in untreated controls, and it was greatest for CaCl2-infused carcasses. Calcium chloride-infused carcasses had lower (P < 0.01) NAD and higher (P < 0.001) NADPH concentrations than water- and ZnCl2-infused or untreated control carcasses. The negative effects of calcium infusion on fresh lamb color, higher (P < 0.01) metmyoglobin accumulation rate, and lower (P < 0.01) L*, a*, and b* color measurements could be explained by the lower amounts of unbound water (P < 0.01), shorter sarcomere length (P < 0.01), lower NAD concentrations (P < 0.01), and higher lipid peroxidation (P < 0.01). Zinc and water-infusions produced less (P < 0.01) lipid oxidation and improved the color and color stability of fresh lamb (P < 0.001). Rate of lipid oxidation in LM chops was greater (P < 0.01) after 3 wk of vacuum-packaged storage than 24-h postmortem. Metmyoglobin-reducing activities (sarcoplasmic and myofibrillar) were decreased in response to infusion treatments (P < 0.001), and ZnCl2 infusion resulted in the lowest metmyoglobin-reducing activities (P < 0.001). A significant association between the myofibrillar metmyoglobin-reducing activity and lipid peroxidation was observed, but metmyoglobin-reducing activities were not associated with any improvement in lamb color. Strategies to increase the antioxidant levels in lamb are very important to improve lamb quality, especially during vacuum-packaging storage.

Metmyoglobin reducing activity.

Meat colour is a major factor that influences the purchase decision by consumers. Many intrinsic and extrinsic factors contribute to the final colour of meat. The role of the MetMb reducing system in maintaining meat colour has been controversial and a considerable amount of work has been published since [Giddings, G. G., 1974. Reduction of ferrimyoglobin in meat. CRC Critical Reviews in Food Technology 5, 143-173] classic review. Historically, the activity of MetMb reductase was classified under different names, for example, diaphorases, aerobic and anaerobic reducing systems, cytochrome b(5) MetMb reductase, and NADH dependent metmyoglobin reducing enzyme system. Several techniques have been proposed to measure the enzyme activity including reflectance spectrophotometry and absorbance spectrophotometry. However, the variations in the reductase systems and techniques used to measure them have yielded inconsistent results from different investigators. This review seeks to characterize the current understanding of metmyoglobin reduction in meat especially with reference to recent developments in this area. Because many systems (different enzymatic systems and non-enzymatic systems) have been reported to reduce MetMb, the term MetMb reductase is not appropriate to be used to reflect "the MetMb reducing activity" in meat. The need for a standardized approach for measuring MetMb reduction is discussed in order for future research to ensure a greater understanding of this important reaction.

Effect of preslaughter feed withdrawal period on longissimus tenderness and the expression of calpains in the ovine.

The objective was to study the role of calpains in meat tenderness. Lambs were fasted for various periods of time to generate differences in meat tenderness and to determine in tandem the expression of calpain 1, calpain 2, calpain 3, and calpastatin. The assumption has been that increased calpain expression associated with an increase in tenderness indicates a role for calpain in the tenderization process and vice versa. Fasting lambs for 1 day caused a significant improvement in longissimus (LD) tenderness compared to the control. Correlations between the tenderness of the LD and the expression of the calpains and calpastatin were significant for calpains 1 and 3 but not for calpain 2 or calpastatin. Consequently, this study supports a role for calpains 1 and 3, but not for calpain 2, in the tenderization of the LD from fasted lambs during post-mortem aging.

Metmyoglobin reducing activity and colour stability of ovine longissimus muscle.

Characteristics of metmyoglobin reducing activity in ovine longissimus were determined, and its effect on colour and colour stability of muscle was investigated in two experiments. In the first experiment vacuum packed ovine longissimus samples were incubated at 5-35°C during the first 16 h post mortem (n=8 per treatment). Metmyoglobin reducing activity was negatively affected by incubation temperatures above 30°C, but colour and colour stability were little affected at 24 h post mortem and after 2 weeks of vacuum storage at 2°C. In the second experiment the effects of pre-slaughter stress and electrical stimulation on metmyoglobin reducing activity, colour and colour stability of ovine longissimus (n=40) with an ultimate pH below 5.8 were investigated. Neither of the treatments had an effect on metmyoglobin reducing activity or colour parameters. The relatively large variation in metmyoglobin activity and colour parameters allowed correlation analysis. Metmyoglobin reducing activity was not correlated to colour or the colour stability parameters. The results of the present study indicate that metmyoglobin reducing activity is not the primary determinant of colour or colour stability of ovine longissimus muscle.

Impact of introducing specifications on the tenderness of retail meat.

Over a 3-year period (1997-1999), the shear force of 4371 retail beef, lamb and pork midloin samples collected from 363 retail outlets were tested using a MIRINZ tenderometer. Information about aging time, processor and retail chain was recorded. Consumers (n=2313) were also surveyed on their perception of the tenderness of beef and lamb midloin samples with known shear force. The results validated that shear force, as measured by the MIRINZ tenderometer, could be used to create instrumental tenderness categories which reflected consumer perceptions of tenderness. Over the 3-year sampling period, the shear force of beef and lamb decreased by 21.9 and 17.2%, respectively, and there was a consistent decrease in the number of 'tough' samples. The improvement in tenderness coincided with the introduction of a Quality Mark program in 1997 for beef and lamb and 3 years of implementation by auditing. The Quality Mark program sets specifications for the quality of retail meat in New Zealand and guidelines to achieve these specifications. In comparison to retail beef and lamb, the shear force of retail pork decreased marginally by 7.9%. Furthermore, the decrease in the number of 'tough' pork samples was not consistent over the testing period. Analysis of these data showed that for all three meats a considerable improvement in tenderness can be achieved by adopting a minimum post-slaughter aging time and optimizing the processing conditions.

Evidence against the non-enzymatic calcium theory of tenderization.

The objective of the present study was to determine whether variation in the tenderization of lamb longissimus could be attributed to variations in the rise in free calcium postmortem and sarcomere lengthening post rigor. The longissimus muscle of 10 crossbred lambs (Romney×Coopworth) was sampled at 1 and 7 days postmortem for determination of MIRINZ shear force, myofibrillar fragmentation index (MFI), sarcomere length, free calcium, and proteolysis of troponin-T. Despite considerable variation in tenderness and tenderization of the muscles, sarcomere lengthening was not observed. The concentration of free calcium at 7 days postmortem correlated significantly with the MFI (r=0.640; P<0.05) and tended to correlate with the shear force (r=-0.596; P<0.1) and degradation of troponin-T (r=0.625; P<0.1). Degradation of troponin-T was significantly correlated with tenderization (r=0.664; P<0.05). Troponin-T is a calpain substrate, but reportedly is not degraded through a direct effect from calcium. The present results, therefore, suggest that the variation in free calcium in postmortem muscle affects tenderization through an effect on the calpain system and not through a direct effect of calcium on myofibrillar proteins. Consequently, the results of this study do not support the (calcium) theory that calcium directly affects tenderization.