Effect of NaCl on thermal aggregation of egg white proteins from duck egg

Thermal aggregation of duck egg white solution (1 mg protein/ml, pH 7) was monitored in the presence of different NaCl concentrations (0–6%, w/w) across the temperature range of 20–90 °C. Duck egg white solution exhibited higher turbidity with coincidental increases in surface hydrophobicity and decreases in sulfhydryl group content as temperatures increased from 70 to 90 °C (p < 0.05). As NaCl concentration increased, the negative charge decreased, with coincidental increases in particle size of aggregate after heating to 90 °C. As visualised by confocal laser scanning microscopy, larger clusters of protein aggregates were observed with increasing NaCl concentrations. Major duck egg white protein with molecular mass of 45 kDa disappeared in the presence of 2–6% NaCl after heating above 80 °C, regardless of concentrations. Therefore, NaCl, especially at high concentrations, could induce thermal aggregation of duck egg white protein, which could determine the characteristics of salted egg white after heating.     

Effects of prolonged heating on antioxidant activity and colour of honey

The kinetics of changes in total antioxidant activity as assessed by DPPH radical and brown pigment formation (BPF) in honey heated at different temperatures (50, 60 and 70 °C) for up to 12 days were studied. Antioxidant activity and BPF increased with treatment temperature and time. BPF increased following zero-order kinetics with the activation energy value of 122 kJ/mol⁻¹ at 50–70 °C. However, antioxidant activity variation showed different trends according to heating temperatures following second-order, first-order and zero-order kinetics at 50, 60 and 70 °C, respectively. Heating of honey at 70 °C was found to be more effective than 50 and 60 °C for both two parameters. The results demonstrated that antioxidant activity was correlated with increased browning of the samples.     

Relationship between meat toughness and properties of connective tissue from cows and young bulls heat treated at low temperatures for prolonged times

The aim of the current study was to elucidate whether cows and young bulls require different combinations of heating temperature and heating time to reduce toughness of the meat. The combined effect of heating temperature and time on toughness of semitendinosus muscle from the two categories of beef was investigated and the relationship to properties of connective tissue was examined. Measurements of toughness, collagen solubility, cathepsin activity and protein denaturation of beef semitendinosus heated at temperatures between 53 °C and 63 °C for up to 19 1/2 h were conducted. The results revealed that slightly higher temperatures and prolonged heating times were required to reduce toughness of semitendinosus from cows to the same level as in young bulls. Reduced toughness of semitendinosus as a result of low temperature for prolonged time is suggested to result from weakening of the connective tissue, caused partly by denaturation or conformational changes of the proteins and/or by solubilization of collagen.     

Effects of dry,vacuum, and special bag aging; USDA quality grade; and end-point temperature on yields and eating quality of beef Longissimus lumborum steaks

This study evaluated the effects of three aging methods: (dry (D), wet (W), and special bag (SB)); two quality grades [USDA Choice((≥ Small⁵⁰ marbling) and Select); and two cooked end-point temperatures (62.8 °C and 71.1 °C) on physico-chemical traits of instrumental tenderness, color, and sensory properties of Longissimus lumborum beef muscle. Dry-aged loins had higher (P < 0.0001) weight loss than W or SB aged loins. However, D and SB aged loins had similar (P > 0.05) combined losses. W aged loins had higher (P < 0.01) L* values than D or SB aged loins. Warner–Bratzler shear force of steaks was not affected (P > 0.05) by aging method or quality grade but increased (P < 0.0001) as end-point temperature increased. Sensory panel evaluation also showed no effect (P > 0.05) of aging method or quality grade on myofibrillar tenderness, juiciness, connective tissue amount, overall tenderness or off flavor intensity. Steaks cooked to 62.8 °C were juicier (P < 0.05) than those cooked to 71.1 °C. Neither D nor SB aging had advantages over W aging.     

Effect of endogenous ascorbic acid oxidase activity and stability on vitamin C in carrots (Daucus carota subsp. sativus) during thermal treatment

The purpose of this research was to study the effect of endogenous ascorbic acid oxidase (AAO) on vitamin C in carrots (Daucus carota subsp. sativus), namely Nantes, Egmont Gold and baby carrots during thermal treatment. Enzyme-substrate reaction kinetics of AAO were described using Michaelis–Menten equation. The estimated K_m and V_max values of AAO ranged from 50.34 to 63.54 μM and 23.70 to 26.82 μmol/min, respectively. Nantes carrots had the lowest AAO activity. On the other hand, Egmont Gold had the highest V_max. AAO activity in all carrot cultivars was stable up to 50 °C and inactivated above 50 °C. Irreversible thermal inactivation of AAO followed first order kinetics (55–70 °C) and the estimated activation energy of the three carrot cultivars situated between 114.33 and 191.45 kJ/mol. Regarding vitamin C stability, thermal treatment at 60–70 °C has resulted in total conversion of l-AA to DHAA due to residual AAO activity; a complete AAO inactivation was found in 80 °C-treated carrots with high vitamin C retention predominantly in l-AA form, up to 90%. On average, the carrots had a total vitamin C content amounting from 368.24 to 379.87 μg/g dry matter and the Nantes carrots had the highest vitamin C content. The effectiveness of rapid inactivation of endogenous AAO via heating (>80 °C, 10 min) prior to matrix disruption gave protection to l-AA towards enzymatic oxidation, thus resulted in a higher vitamin C content and stability in carrots.     

Influence of lamb age and high-oxygen modified atmosphere packaging on protein polymerization of long-term aged lamb loins

The objective of this study was to determine the influence of lamb age and high-oxygen modified atmosphere (HiOx-MAP) on tenderness of loins during display. Loins from 36 carcasses of two different age groups [4-month-old (New season; NS) and 11-month-old lambs (Old season; OS)] were vacuum-packaged and stored for 8 weeks at −1.5 °C. After storage, the loins were cut into 6-cm thick chops, assigned to either HiOx-MAP or oxygen-permeable overwrap-PVC, and then displayed for 8 days at 3 °C. Initially, packaging methods did not influence shear force (P > 0.05). However, at the end of display, a significant increase in shear force and lipid oxidation was found in OS loins under HiOx-MAP. SDS–PAGE and Western blot results found a greater extent of cross-linked myosin products from OS loins in HiOx-MAP compared to NS loins. These results suggest that HiOx-MAP can adversely influence meat quality of fully-tenderized loins, and meat from older lamb may be more susceptible to an oxidizing environment of HiOx-MAP.     

Bovine cathepsin D activity under high pressure

The stability and catalytic activity of bovine cathepsin D in Bis-Tris buffer (pH 6.0) in different pressure–temperature domains (0.1–650 MPa, 20–75 °C) were investigated and described with mathematical models. Cathepsin D inactivation followed first-order kinetics at all pressure–temperature conditions tested. The protease was largely pressure stable at room temperature and heat stable at ambient pressure up to 300 MPa and 55 °C, respectively, causing less than 10% inactivation after 10 min treatment. Pressure and temperature act synergistically on the enzyme inactivation under most conditions. However, at 100 MPa a significant stabilisation of the enzyme against temperature-induced inactivation was observed. Pressure drastically inhibited the cleavage of a synthetic substrate by cathepsin D in Bis-Tris buffer (pH 6.0) causing a reduction of the catalytic rate of more than 50% at 100–400 MPa. Maximal substrate cleavage by cathepsin D was identified at 60 °C and ambient pressure conditions after 20 min treatment.     

Structural and biochemical characteristics of bovine intramuscular connective tissue and beef quality

The aim of the study was to evaluate the impact of structural and biochemical characteristics of muscle intramuscular connective tissue on beef quality. The experimental design was based on three muscles of three breeds sampled as fresh material and cooked at 55 °C (Longissimus thoracis and Semimembranosus) or at 70 °C (Semimembranosus and Biceps femoris) for quality assessment. The results showed that muscle characteristics influence beef quality differently from one muscle to another. In grilled LT, proteoglycan content contributed negatively to juiciness, and intramuscular lipids were linked positively to tenderness, flavour, residues and overall liking scores. In grilled SM, cross-link and lipid contents were involved in beef quality. In BF cooked to 70 °C, perimysial branch points were negatively linked to tenderness. In SM cooked to 70 °C, perimysial area was involved in beef quality. These results should allow a better understanding of the factors involved in background toughness, in juiciness and flavour of meat.     

Pineapple fruit bromelain affinity to different protein substrates

Optimal pH and temperature conditions for proteolytic activity of pineapple fruit bromelain were determined using five different substrates: azocasein and azoalbumin (pH 3–10 at 20–70 °C), casein and sodium caseinate (pH 2–10 at 20–70 °C), and haemoglobin (pH 2–6.5 at 30–60 °C). Fruit bromelain has shown optimum activity at pH 7.5 for azoalbumin and at 6.5 for azocasein, all at 55 °C. Fruit bromelain activity determined with casein and sodium caseinate has shown optimum activity at 59 °C, while the optimum pH was 7.7 for casein and 6.5 for sodium caseinate. Optimum hydrolysis conditions of fruit bromelain towards haemoglobin showed a sharp peak at an acidic pH 2.9 at 37 °C. The lowest results of K_m and the highest results of V_max/K_m were found for azocasein and azoalbumin. These substrates are highly recommended for fruit bromelain activity determination.     

Effects of temperature,solid content and pH on the stability of black carrot anthocyanins

Anthocyanin stability of black carrots was studied at various solid contents (11, 30, 45 and 64° Brix) and pHs (4.3 and 6.0) during both heating, at 70–90 °C, and storage at 4–37 °C. Monomeric anthocyanin degradation fitted a first-order reaction model. Degradation of monomeric anthocyanins increased with increasing solid content during heating, while it decreased during storage. For example, at pH 4.3, half-life periods for anthocyanins at 30, 45 and 64° Brix were, respectively, 8.4, 6.9 and 5.2 h during heating at 80 °C and 18.7, 30.8 and 35.9 weeks during storage at 20 °C. At 30–64° Brix, increasing pH from 4.3 to 6.0 enhanced the degradation of anthocyanins during heating. The effect of pH on thermal stability of anthocyanins was also studied at six different pHs (2.5–7.0) in citrate-phosphate buffer solutions and significant decrease in anthocyanin stability was observed at pHs above 5.0. Higher activation energies (E_a) were obtained during heating than during storage with increasing solid contents. At 30–64° Brix, E_a values ranged from 68.8 to 95.1 kJ mol⁻¹ during heating and from 62.1 to 86.2 kJ mol⁻¹ during storage. Q₁₀ values at 20–37 °C were as high as 3.1 at 45° Brix and 3.6 at 64° Brix.     

鸭胸肌肉加热过程中肌动球蛋白解离研究

为了解鸭胸肌肉加热过程中肌动球蛋白变化情况,本实验以鸭胸肉为材料,研究了加热温度（45、50、55、60、65、70 ℃）和加热时间（0、1、10、20、30、60 min）对肉中肌动球蛋白解离的影响。采用蛋白质免疫印迹技术测定肌动蛋白的含量。结果表明：在45 ℃加热条件下,肌动球蛋白几乎未发生解离（P＞0.05）;而在50、55 ℃或60 ℃加热条件下,随着加热时间的延长,肌动蛋白含量先增加后降低,但均较对照组显著性增加（P＜0.05）;65 ℃加热60 min,肌动蛋白含量降至对照组水平;70 ℃加热条件下,加热时间为30 min或60 min,检测不到肌动蛋白的存在。因此,加热温度为50～60 ℃,加热时间为10～30 min时能显著促进肌动球蛋白解离。     

Strategy to inactivate Clostridium perfringens spores in meat products

The current study aimed to develop an inactivation strategy for Clostridium perfringens spores in meat through a combination of spore activation at low pressure (100–200 MPa, 7 min) and elevated temperature (80 °C, 10 min); spore germination at high temperatures (55, 60 or 65 °C); and inactivation of germinated spores with elevated temperatures (80 and 90 °C, 10 and 20 min) and high pressure (586 MPa, at 23 and 73 °C, 10 min). Low pressures (100–200 MPa) were insufficient to efficiently activate C. perfringens spores for germination. However, C. perfringens spores were efficiently activated with elevated temperature (80 °C, 10 min), and germinated at temperatures lethal for vegetative cells (≥55 °C) when incubated for 60 min with a mixture of l-asparagine and KCl (AK) in phosphate buffer (pH 7) and in poultry meat. Inactivation of spores (∼4 decimal reduction) in meat by elevated temperatures (80–90 °C for 20 min) required a long germination period (55 °C for 60 min). However, similar inactivation level was reached with shorter germination period (55 °C for 15 min) when spore contaminated-meat was treated with pressure-assisted thermal processing (568 MPa, 73 °C, 10 min). Therefore, the most efficient strategy to inactivate C. perfringens spores in poultry meat containing 50 mM AK consisted: (i) a primary heat treatment (80 °C, 10 min) to pasteurize and denature the meat proteins and to activate C. perfringens spores for germination; (ii) cooling of the product to 55 °C in about 20 min and further incubation at 55 °C for about 15 min for spore germination; and (iii) inactivation of germinated spores by pressure-assisted thermal processing (586 MPa at 73 °C for 10 min). Collectively, this study demonstrates the feasibility of an alternative and novel strategy to inactivate C. perfringens spores in meat products formulated with germinants specific for C. perfringens.     

Enzymatic hydrolysis of granular native and mildly heat-treated tapioca and sweet potato starches at sub-gelatinization temperature

The effect of mild heat treatment (below gelatinization temperature) towards the susceptibility of granular starch to enzymatic hydrolysis was investigated. Tapioca and sweet potato starches were subjected to enzymatic hydrolysis with a mixture of fungal α-amylase and glucoamylase at 35 °C for 24 h. Starches were hydrolyzed in native (granular) state and after heat treatment below gelatinization temperature (60 °C for 30 min). The dextrose equivalent (DE) value of heat-treated starch increased significantly compared to native starch, i.e., 36–50% and 27–34% for tapioca and sweet potato starch, respectively. Scanning electron microscopy examination showed that enzymatic erosion occurred mainly at the surface of starch granules. Hydrolyzed heat-treated starch exhibited rougher surface and porous granules compared to native starch. X-ray analysis suggested that enzymatic erosion preferentially occurred in amorphous areas of the granules. The amylose content, swelling power and solubility showed insignificant increase for both starches. Evidently, heating treatment below gelatinization temperature was effective in enhancing the degree of hydrolysis of granular starch.     

Decomposition kinetics of umami component during meat cooking

We developed a kinetic model for the decomposition reaction of inosine monophosphate (IMP), which is a umami component, and obtained kinetic parameters based on the amount of IMP in an isothermal experiment. The amount of remaining IMP decreased with heating time, and its reduction rate was the highest at 40 °C. We assumed that the activity of IMP decomposition enzyme is temperature-dependent above 40 °C, and constant below 40 °C. The predicted results using this kinetic model are in good agreement with the experimental ones. Unsteady-state three-dimensional heat transfer analysis of meat during sous-vide cooking was conducted, and the distribution of remaining IMP was predicted. By the end of sous-vide cooking, the ratio of the amount of IMP in the interior of the meat decreased, whereas at the surface region, it was almost the same as the initial value, because the surface temperature reached the inactivation temperature immediately.     

Dissociation of natural actomyosin from kuruma prawn muscle induced by pyrophosphate

Effect of pyrophosphate (PP) on the dissociation and stability of natural actomyosin (NAM) from kuruma prawn muscle was studied in comparison with adenosine 5′-triphosphate (ATP). In the presence of PP up to 5 mM, NAM exhibited lower Mg²⁺-ATPase activity (P < 0.05), while no marked change was observed in NAM treated with ATP at all concentrations tested (0.25–10 mM) (P > 0.05). Ca²⁺-ATPase activity of NAM treated with 5 mM PP decreased markedly when incubated at temperatures greater than 30 °C, suggesting lowered thermal stability of the liberated myosin molecule. Nevertheless, Ca²⁺-ATPase activity of ATP-treated NAM was similar to the control NAM. In the presence of 5–10 mM MgCl₂, NAM treated with 5 mM PP underwent dissociation effectively, as evidenced by a greater decrease in Mg²⁺-ATPase activity as well as an increased band intensity of actin released. Therefore, addition of PP in combination with MgCl₂ was more effective than was ATP in dissociating the actomyosin complex of prawn muscle.     

Pacific whiting (Merluccius productus) underutilization in the Gulf of California: Muscle autolytic activity characterization

In México’s Northwest coast, Pacific whiting (Merluccius productus) is considered an under-utilized species because of its high tendency to become parasitized, thus promoting a high proteolytic activity present in muscle tissue. Sample fish for study were separated in lots by degree of parasitism in “apparent” parasitized (APP) and advanced parasitized (ADP). Thus, pH and temperature conditions of mayor endogenous proteolytic activity in muscle were determined. Maximum activity was detected at 50 °C (pH 3.5–4.0) and at 60 °C (pH 6.75–7.0). Parasitism degree had a significant effect in enzyme activity at acidic pH (p < 0.05) being higher in APP at low temperature (30 °C). Higher temperatures (40–50 °C) favored (p < 0.05) activity in ADP muscle (same pH range) with the highest (p < 0.05) observed at 50 °C at pH 3.5. No much difference was observed at pH 7.0–8.0. Results suggest that pH around physiological conditions at 60 °C could be used as an advantage in fish protein hydrolysate production or as processing aid where a protein hydrolysis is required.     

Oxidation desensitizes actomyosin to magnesium pyrophosphate-induced dissociation

This study aimed to establish the influence of protein oxidation on the ability of magnesium pyrophosphate (PP) to dissociate actomyosin. Actomyosin isolated from pork muscle then suspended in 0.1 M NaCl at pH 6.2 was oxidatively stressed with 10 μM FeCl₃/0.1 mM ascorbate/1 mM H₂O₂ for 6 or 12 h at 4 °C. Protein oxidation was evidenced by the loss of myosin and actin, the concomitant formation of disulphide-cross-linked polymers, and elevated myosin ATPase activity. The intrinsic viscosity of oxidized actomyosin had a weaker response to PP-Mg²⁺ than that of non-oxidized actomyosin, indicating the suppression of actomyosin dissociation. Moreover, oxidized actomyosin solutions were devoid of small particles (<10 nm) and the stressed actomyosin exhibited weaker binding of PP-Mg²⁺ than non-oxidized, which further suggested a reduced myosin–PP interaction and subsequent dissociation of the actomyosin complexes.     

Colour and sarcoplasmic protein evaluation of pork following water bath and ohmic cooking

The objective of this study was to investigate the effects of ohmic (OH) and waterbath (WB) cooking on colour attributes and sarcoplasmic changes of porcine longissimus dorsi muscle at the same endpoint temperatures (EPTs; range 10 °C–80 °C). The OH treatment was carried out at 10 V cm^− 1, and the WB temperature at 85 °C. The colour parameters, deoxymyoglobin% (DeoMb) and metmyoglobin% (MetMb) of the OH-cooked meat were significantly lower (P < 0.05) than those obtained by WB-cooking at the same EPTs (range 60 °C–80 °C). SDS-PAGE analysis showed that the meat treated with WB-cooking had a lower sarcoplasmic protein solubility (5.97 mg/g vs.14.89 mg/g, P < 0.05) and fainter protein bands than that of OH-cooking thus, indicating paler colour, and lower water-holding capacity especially in WB-cooked meat at EPTs above 40 °C. Strong correlations among lightness, browness, metmyoglobin% and soluble proteins were observed in meat following OH-cooking.     

Artocarpus integer leaf protease: Purification and characterisation

The presence of a protease in Artocarpus integer leaves, which are traditionally used as a meat tenderiser, was verified by the presence of a band at 69 kDa, using caseinolytic zymography. Purification by temperature phase partitioning with Triton X-114, ammonium sulphate precipitation and gel filtration chromatography yielded a preparation with a 12-fold increase in enzyme purity and a final specific activity of 76.67 U/mg. The cysteinic nature of this enzyme was confirmed through inhibition of enzyme activity by E-64 and iodoacetamide and enhancement of activity by cysteine and 2-mercaptoethanol. The protease retained 70% of its activity over a broad pH range (pH 6–12), with optimal activity recorded at pH 10 and 40 °C. The enzyme was stable at temperatures up to 70 °C, with 80% of its activity intact. Addition of 5 mM Ca²⁺ stimulated enzyme activity and a kinetic study of the enzyme yielded K_m and V_max values of 0.304 mg/mL and 0.735 mg/mL/min, respectively.     

“Cold” electroporation in potato tissue induced by pulsed electric field

This work compares PEF-induced effects in potato tissue at temperatures below and above ambient (T = 2–45 °C). The potato (Agata) was selected for investigation. The PEF treatment using electric field strength E = 200–800 V/cm and bipolar pulses of near-rectangular shape with pulse duration t_p (=100 μs) was applied. The PEF experiments were done under non-isothermal conditions with temperature increase owing to the effect of ohmic heating. The linear temperature dependencies of electrical conductivity of potato tissue with different values of the electrical conductivity disintegration index, Z, were observed. However, the values of the conductivity temperature coefficient, α, at the reference temperature T_r = 25 °C were noticeably different for the intact (α_i = 0.0255 ± 0.0003 °C⁻¹) and completely damaged (α_d = 0.031 ± 0.009 °C⁻¹) potato tissues. This difference was explained by the impact of temperature on the structure of the damaged tissue. The non-isothermal PEF treatment was shown to be an effective tool for electroporation at low temperatures (below ambient). For initial temperature T_i = 2 °C, the most power saving was the PEF treatment at E = 200 V/cm (W ≈ 20–30 kJ/kg), and the PEF treatment at E = 400–800 V/cm required more power consumption (W ≈ 50–80 kJ/kg). The PEF treatment at the fixed value of E (=400 V/cm) showed that the total power consumptions (accounting for PEF treatment and thermal heating), required for high level of tissue disintegration, Z ≈ 0.9, were comparable for initial temperatures T_i = 2 °C (W ≈ 50–80 kJ/kg) and T_i = 20 °C (W ≈ 80 kJ/kg) and were noticeably higher for initial temperature T_i = 40 °C (W ≈ 150 kJ/kg).