塑料厂区DEHP的污染及蔬菜安全评价

邻苯二甲酸二(2-乙基己基)酯(DEHP)具有致畸致癌的作用,对塑料附近农田蔬菜进行了采样调查,应用GC/MS联机检测技术检测了12种蔬菜样品中DEHP的浓度水平。结果表明,按照EPA提出的人体每天限制剂量(RfD)为20μg/kg体重,则塑料工业区蔬菜DEHP含量已经超出安全标准。蔬菜不同品种累积DEHP的能力大不相同,其中冬瓜、茄子、毛豆、小白菜累积DEHP含量较高,为重污染蔬菜品种;番茄、小辣椒、丝瓜累积DEHP含量较低,在塑料厂周边农田种植和食用相对较安全。     

Absorbability of Calcium from Brassica Vegetables: Broccoli, Bok Choy, and Kale

Absorption of calcium from three intrinsically labeled Brussica sp. vegetables was measured in 15 normal women in a three-way randomized design. The test load of calcium was about 83 mg for each source. Fractional calcium absorption from broccoli averaged 0.478 ± 0.089, from bok choy stems, 0.519 ± 0.089, from bok choy leaves, 0.520 ± 0.074, and from kale 0.527 ± 0.091. These differences were both absolutely small and statistically insignificant. Mean absorbability of milk calcium ingested at the same load has been previously shown to be 0.463 ± .095. This value is slightly but significantly lower than the average value for the Brassica sources combined (0.514 ± 0.090). Thus, Brussicu vegetable sources exhibit excellent calcium bioavailability.     

Effect of Stir Frying on the Antioxidant Capacity and Aroma Components of Bok Choy (Chinese Cabbage)

Bok choy, Brassica rapa subsp. Chinensis, is a type of Chinese cabbage. Stir frying could affect antioxidant activity and aroma composition of bok choy. Antioxidant activity such as diphenyl picryl hydrazinyl radical and ferric-reducing antioxidant power of the leave and stem samples were determined. The highest ferric-reducing antioxidant power activity was obtained at 1.5 min stir-frying under 160ºC for bok choy leaves (49.7 ± 2.1 µmol FeSO₄/g dry weight). In ferric-reducing antioxidant power assay, antioxidant capacities of bok choy stem samples increased significantly after stir-frying. Dimethyl sulfide (DMS), a typical volatile organic sulfur compound with a characteristic cabbage-like odor, was only observed in leave groups. After cooking treatment, antioxidant activities of bok choy stems were higher than those of leaves in diphenyl picryl hydrazinyl radical assay. Odor-active compounds were identified using gas chromatography-olfactometry-mass spectrometry technique. Compared to stem sample data, more aroma components were quantified in leaves sample in 160, 180, and 210ºC, respectively. It was first time to detect and analysis the aroma components and antioxidant activity in different edible part of bok choy after Chinese domestic cooking.     

硒对常见蔬菜种子萌发的影响及在植株中的分布

分析不同质量浓度的Na2SeO3对蔬菜种子萌发的影响及硒在蔬菜不同器官中的分布,采用种子萌发实验和盆栽实验,应用氢化物发生-原子荧光法测定总硒,透析法分析有机硒。结果表明：随着Na2SeO3质量浓度的升高,蔬菜种子的发芽势、发芽率、简易活力指数、发芽指数均呈先上升后下降的趋势,但个体之间存在一定差异。绿豆在2.5 mg/L的处理液条件下各项活力指标达到最好,但随着Na2SeO3质量浓度升高,其各项指标开始下降。蔬菜植株中总硒含量随着浇灌液中Na2SeO3质量浓度的增加呈明显的上升趋势,在10.0 mg/L的高硒环境下对硒的富集能力为：上海青＞快菜＞茄子＞辣椒＞西红柿。茄子、辣椒、西红柿3 种蔬菜不同部位中硒含量分布存在显著差异,其中m（有机硒）≥1/2m（总硒）。实验结果可为筛选最适宜水培液中Na2SeO3质量浓度和选择适宜培育的富硒蔬菜种类,以及选择硒含量高的部位进食提供理论依据。     

Uptake of di-(2-ethylhexyl)phthalate from plastic mulch film by vegetable plants

The uptake of di-(2-ethylhexyl) phthalate (DEHP) from plastic mulch film used in field cultivation by 10 vegetable plants was investigated by experiments carried out in pots. The results showed that DEHP was transferred from the mulch film to all vegetable plants. Wax gourd (Benincasa hispida) showed the greatest capacity for uptake of DEHP, while cucumber (Cucumis sativus) and pumpkin (Cucurbita moschata) could also accumulate high levels. This implies that wax gourd, cucumber and pumpkin may be sources of DEHP contamination in the human diet. Moreover, Chinese cabbage (Brassica parachinensis) also accumulated a high level of DEHP from mulch plastic film giving dietary exposure close to the daily intake limit for DEHP.     

Residual polyphenol oxidase and peroxidase activities in high pressure processed bok choy (Brassica rapa subsp. chinensis) juice did not accelerate nutrient degradation during storage

Polyphenol oxidase (PPO) and peroxidase (POD) cannot be fully inactivated by commercial high pressure processing (HPP) operations, and their residual activities may accelerate nutrient degradation during storage. This study hence aimed to establish the effect of residual enzyme activity on nutrient preservation in bok choy (Brassica rapa subsp. chinensis) juice. Bok choy juice was treated at 600 MPa for up to 20 min and enzyme inactivation, nutrient retention immediately after treatment and nutrient preservation during storage were determined. High residual PPO (85.1 ± 2.6%) and POD (68.5 ± 1.0%) activities remained after 20 min of treatment. Increasing the pressure holding time to enhance enzyme inactivation did not compromise total antioxidant capacity, vitamin C, carotenoids, isothiocyanates and vitamin K levels. Neither did it significantly reduce the vitamin C degradation rate during refrigerated storage. Maximising enzyme inactivation may thus not be necessary for nutrient preservation during the storage of HPP-treated bok choy juice.Industrial relevance textWith HPP, an increase in pressure or holding time is required to achieve higher levels of enzyme inactivation. Without the need to maximize PPO and POD inactivation, juice processors may employ the minimum pressure and holding time required for microbial inactivation. As vegetative bacteria are typically less resistant to HPP inactivation than these enzymes, this could translate to reduced energy costs and increased throughput.     

Di-(2-ethylhexyl) adipate and 20 phthalates in composite food samples from the 2013 Canadian Total Diet Study

A sensitive and selective GC-MS method was developed and used for simultaneous analysis of di-(2-ethylhexyl) adipate (DEHA) and 20 selected phthalates in the food samples from the 2013 Canadian Total Diet Study. At least one of the 21 target chemicals was detected in 141 of the 159 different food composite samples analysed. However, only seven of the 21 target chemicals were detected, with di-(2-ethylhexyl) phthalate (DEHP) and DEHA being detected most frequently, in 111 and 91 different food composite samples, respectively, followed by di-n-butyl phthalate (DBP) (n = 44), n-butyl benzyl phthalate (BBzP) (32), di-iso-butyl phthalate (DiBP) (27), di-ethyl phthalate (DEP) (3), and di-cyclohexyl phthalate (DCHP) (1). Levels of DEP (di-ethyl phthalate), DiBP, DBP, BBzP and DCHP were low, in general, with average concentrations of 9.63, 8.26, 23.2, 12.4 and 64.9 ng g^–1, respectively. Levels of DEHA and DEHP varied widely, ranging from 1.4 to 6010 ng g^–1 and from 14.4 to 714 ng g^–1, respectively. High levels of DEHA were found mainly in the composite samples where the individual food items used to prepare the composite were likely packaged in polyvinyl chloride (PVC) wrapping film, while the highest DEHP levels were found in the vegetable and fruit samples.     

Fungi and mycotoxins in cowpea (Vigna unguiculata L) on Nigerian markets

ABSTRACT

In this study, 81 samples of two cowpea varieties (brown: 54; white: 27) collected from various markets in southwestern Nigeria were examined for fungal and mycotoxin contamination. Moulds belonging to Aspergillus, Fusarium, and Penicillium were recovered from 99% of the samples. In both cowpea varieties, Aspergillus (52–53%) dominated Fusarium (29–30%) and Penicillium (17–20%). The interactive effect of cowpea variety and sampled location was significant (p = .013) on the occurrence of Fusarium species. Aflatoxins were detected in one brown and two white cowpea samples at concentrations reaching 209 and 84 µg/kg, respectively. Additionally, beauvericin was found in two samples of each cowpea variety, albeit at low concentrations. Cowpea presents as an alternative vegetable protein source to groundnuts in household nutrition with respect to mycotoxin contamination. Simple techniques to prevent mycotoxins in dry cowpeas are discussed.     

Nitrate and nitrite content in organically cultivated vegetables

The nitrate and nitrite content of leaf vegetables (Swiss chard, sea beet, spinach and cabbage), “inflorescence” vegetables (cauliflower) and fruit vegetables (eggplant and vegetable marrow) grown with organic fertilizers have been determined by a modified cadmium–Griess method. Samples were purchased from organic food stores as well as collected directly from an organic farm in Madrid (Spain). Nitrate levels were much higher in the leaf vegetables (especially Swiss chard species; average over the different samples and species of 2778.6 ± 1474.7 mg kg^{? 1}) than in inflorescence or fruit products (mean values between 50.2 ± 52.6 and 183.9 ± 233.6 mg kg^{? 1}). Following Swiss chard species, spinach (1349.8 ± 1045.5 mg kg^{? 1}) showed the highest nitrate content, and nitrite was found above the limit of detection in some samples only (spinach, 4.6 ± 1.0 mg kg^{? 1}; sea beet, 4.2 ± 0.7 mg kg^{? 1} and Swiss chard, 1.2 ± 0.4 mg kg^{? 1}). Some vegetables (spinach, cabbage and eggplant) had lower nitrate content in the samples harvested in summer, showing the influence of climatic conditions on the nitrate levels in a plant. The samples taken directly from the organic farm, with the exception of eggplant, had higher or slightly higher average nitrate values than samples purchased in the organic food stores, ranging from 117 to 1077%.     

Study on the influence of temperature,storage time and packaging type on di-n-butylphthalate and di(2-ethylhexyl)phthalate release into packed meals

Ready-to-eat meals packed in polyethylene terephthalate (PET) and aluminium dishes, supplied to patients in two hospitals in the Campania region (Italy), were studied to evaluate the probable migration of di-n-butylphthalate (DBP) and di(2-ethylhexyl)phthalate (DEHP) from the packaging into the food. The influence of temperature, storage time and type of package on the migration process was considered, analysing the meals according to three time ranges, before the packaging (T ₀) and after 60?min (T ₁) and 120?min (T ₂) from packaging during the storage in thermostatic delivery carts. At T ₀ in the meals sampled before packaging in PET dishes, mean levels of DBP and DEHP were 0.023?±?0.002?µg/g and 0.069?±?0.041?µg/g, respectively; the DBP level increased 230% and that of DEHP increased 208% by time T ₀ versus T ₂. In the meals sampled before packaging (T ₀) in aluminium dishes, the mean levels of DBP and DEHP were 0.030?±?0.001?µg/g and 0.057?±?0.015?µg/g, respectively. The significant increase in contaminant levels over storage times for meals packed in PET dishes demonstrates that from packages made of plastic materials the migration of phthalic acid esters into foods is possible. In meals packed in PET dishes, the highest DBP and DEHP increases were observed in the T ₀ to T ₁ range, which represented the time interval over which meals were kept hot, and mainly in the first ones, where the highest temperatures have been recorded.     

小白菜硝酸盐含量与NO3－/NH4+及氮代谢关键酶的相关性

采用液体培养实验研究了不同NO3－与NH4＋浓度比（分别为50∶50、75∶25和100∶0）对10 个品种小白菜（Brassica chinensis L.）的硝酸盐含量、光合系统参数及氮代谢关键酶活性的影响。结果表明,随着硝铵比的增加,小白菜总干质量逐渐增加（除品种天津小白菜和大头清江白菜的总干质量随硝铵比的增加先降低后升高,品种香港春秀甜白菜（236）和正旺达88的总干质量先升高后降低外）,与c（NO3－）∶c（NH4＋）为50∶50比较,增幅分别为12.66%～76.88%（c（NO3－）∶c（NH4＋）为75∶25）和17.98%～95.07%（c（NO3－）∶c（NH4＋）为100∶0）;小白菜叶和根中的硝酸盐含量增加,而叶柄硝酸盐含量则表现出先增加后下降的趋势,小白菜硝酸盐的含量叶柄（3 882.62～5 448.81 mg/kg）＞叶（2 004.86～4 146.50 mg/kg）＞根（505.39～2 188.68 mg/kg）。小白菜叶片中硝酸盐含量与硝酸还原酶活性成显著负相关,而与亚硝酸还原酶和谷氨酰胺合成酶活性成显著正相关。小白菜叶片中硝酸盐的含量随着净光合速率（Pn）和胞间二氧化碳浓度（Ci）的增加而下降,随蒸腾速率（Tr）的增强而增加。     

Legume seed vicilins (7S storage proteins) interfere with the development of the cowpea weevil (Callosobruchus maculatus (F))

Vicilins (7S storage proteins) isolated from the seeds of the legumes Vigna unguiculata (cowpea), Vigna angularis (adzuki bean), Canavalia ensiformis (jack bean), Glycine max (soybean), Phaseolus vulgaris (common bean) and Phaseolus lunatus (lima bean) were shown to be immunologically related and to bind to a chitin matrix. The effect of the isolated vicilins on the development of the cowpea weevil Callosobruchus maculatus was examined. Vicilins from all non-host seeds, including those of the C maculatus-resistant cowpea line IT81D-1045, strongly inhibited larval development (ED₅₀ of 1·07±0·32% to 2·22±0·64%). Vicilins from the C maculatus-susceptible cowpea CE-31 and adzuki bean seeds were the exception with ED₅₀ of 6·25±0·75% and 5·40±1·54%, respectively. These results correlate well with the host range of C maculatus and are possibly a reflection of the low digestibility of vicilins by insect midgut proteinases in addition to the ability they show in binding to chitin-containing structures like the ones found in the bruchid midguts. © 1998 SCI.     

Ambient and indoor particulate aerosols generated by dairies in the southern High Plains

The objectives were to quantify and size ambient aerosolized dust in and around the facilities of 4 southern High Plains dairies of New Mexico and to determine where health of workers might be vulnerable to particulate aerosols, based on aerosol concentrations that exceed national air quality standards. Ambient dust air samples were collected upwind (background) and downwind of 3 dairy location sites (loafing pen boundary, commodity, and compost field). The indoor milking parlor, a fourth site, was monitored immediately upwind and downwind. Aerosolized particulate samples were collected using high-volume sequential reference air samplers, laser aerosol monitors, and cyclone air samplers. The overall (main effects and estimable interactions) statistical general linear model statement for particulate matter (PM₁₀; particulate matter with an aerodynamic diameter of up to 10 μm) and PM_2.5 resulted in a greater mean concentration of dust in the winter (PM₁₀ = 97.4 ± 4.4 μg/m³; PM_2.5 = 32.6 ± 2.6 μg/m³) compared with the summer (PM₁₀ = 71.9 ± 5.0 μg/m³; PM_2.5 = 18.1 ± 1.2 μg/m³). The upwind and downwind boundary PM₁₀ concentrations were significantly higher in the winter (upwind = 64.3 ± 9.5 μg/m³; downwind = 119.8 ± 13.0 μg/m³) compared with the summer (upwind = 35.2 ± 7.5 μg/m³; downwind = 66.8 ± 11.8 μg/m³). The milking parlor PM₁₀ and PM_2.5 concentration data were significantly higher in the winter (PM₁₀ = 119.5 ± 5.8 μg/m³; PM_2.5 = 55.3 ± 5.8 μg/m³) compared with the summer (PM₁₀ = 88.6.0 ± 5.8 μg/m³; PM_2.5 = 21.0 ± 2.1 μg/m³). Personnel should be protected from high aerosol concentrations found at the commodity barn, compost field, and milking parlor during the winter.     

Quality changes in sea urchin (Strongylocentrotus nudus) during storage in artificial seawater saturated with oxygen, nitrogen and air

BACKGROUND: Sea urchin gonads are highly valued seafood that degenerates rapidly during the storage period. To study the influence of dissolved oxygen concentration on quality changes of sea urchin (Strongylocentrotus nudus) gonads, they were stored in artificial seawater saturated with oxygen, nitrogen or air at 5 ± 1 °C for 12 days. RESULTS: The sensory acceptability limit was 11–12, 6–7 and 7–8 days for gonads with oxygen, nitrogen or air packaging, respectively. Total volatile basic nitrogen (TVB‐N) values reached 22.60 ± 1.32, 32.37 ± 1.37 and 24.91 ± 1.54 mg 100 g^?1 for gonads with oxygen, nitrogen or air packaging at the points of near to, exceeding and reaching the limit of sensory acceptability, indicating that TVB‐N values of about 25 mg 100 g^?1 should be regarded as the limit of acceptability for sea urchin gonads. Relative ATP content values were 56.55%, 17.36% and 18.75% for gonads with oxygen, nitrogen or air packaging, respectively, on day 2. K‐values were 19.37%, 25.05% and 29.02% for gonads with oxygen, nitrogen or air packaging, respectively, on day 2. Both pH and aerobic plate count values showed no significant difference (P > 0.05) for gonads with the three treatments. CONCLUSION: Gonads with oxygen packaging had lower sensory demerit point (P < 0.05) and TVB‐N values (P < 0.05), and higher relative ATP content (P < 0.01) and K‐values (P < 0.05), than that with nitrogen or air packaging, with an extended shelf life of 4‐5 days during storage in artificial seawater at 5 ± 1 °C. Copyright © 2011 Society of Chemical Industry     

Myrosinase activity of cruciferous vegetables

Myrosinase activity in partially purified extracts of 12 cruciferous vegetables and an acetone powder preparation of Sinapis alba L. (white mustard) was determined by the initial rate of glucose formation from glucosinolate hydrolysis using a coupled assay. Of the species studied Raphanus sativus L. (radish, 12.8±0.7 μmol min^?1g^?1 powdered tissue) had the greatest myrosinase activity, and Brassica campestris L. ssp. rapifera (turnip) and Nasturtium officinalis R.Br. (watercress) (0.6±0.1 and 0.8±0.03 μmol min^?1g^?1 powdered tissue respectively) the least. The sub-species of Brassica oleracea studied all had similar myrosinase activity (ca 2.5±0.2μmolmin^?1g^?1 powdered tissue) except B. oleracea L. var. gemmifera D.C. (Brussels sprouts) and B. oleracea L. var. capitata L. (white cabbage) which had higher activities (7.6±0.1 and 5.2±0.2μmol min^?1g^?1 powdered tissue respectively). The effect of ascorbate concentration upon the myrosinase activity of six of the crucifers studied and the white mustard preparation, revealed that the ascorbate concentration necessary to promote maximal activity varied with species. A concentration of 0.9mM ascorbate maximally activated radish and turnip myrosinase, while red cabbage, watercress, white mustard and Brussels sprouts were maximally activated at 2.0, 3.0, 5.0 and 0.7–1.0mM ascorbate respectively. Two peaks of maximal myrosinase activity, occurring between 0.9 and 1.0mM and at 3.0mM ascorbate, were found for B. oleracea L. var. botrytis L. subvar. cauliflora D.C. (cauliflower).     

Effect of cellulase/glucanase/xylanase (Roxazyme G2) enzymes combination on nutrients utilisation of vegetable meal (Amaranthus cruentus) fed as sole dietary protein source in rat assay

Amaranthus cruentus vegetable meal (ACVM) had 23% crude protein. Ca, Na, K, Mg and Fe were abundant at 2.0 g kg^?1, 7.1 g kg^?1, 4.8 g kg^?1, 2.5 g kg^?1, 1109 mg kg^?1, respectively. P‐phosporous, oxalates and tannins were noticeable. Lysine, methionine and cystine were limiting. Weight gain for rats on the reference (casein) diet 2 at 6.30 g ±2.87 was highest (P < 0.05) followed by diet 6 (12% ACVM with enzyme supplementation) at 5.01 g ±2.42. Feed intakes were similar (P > 0.05) for rats on the reference diet and for rats on 10% and 12% with/without enzyme supplementation ranging from 42.90 g ± 4.52 in reference diet to 45.12 g ± 3.64. Nitrogen retention was highest for rats on reference diet but similar (P > 0.05) to rats on 12% enzyme supplemented diet at 0.53 ± 1.12 and 0.53 ± 2.10, respectively. Other investigated protein evaluation parameters revealed similar results among rats kept on reference diet and the rats on ACVM based diets with enzyme supplementations. Enzyme supplementation had a complimentary role in ACVM nutrition in rat trial.     

Assessment of average exposure to organochlorine pesticides in southern Togo from water,maize (Zea mays) and cowpea (Vigna unguiculata)

Drinking water, cowpea and maize grains were sampled in some potentially exposed agro-ecological areas in Togo and analysed for their contamination by some common organochlorine pesticides. A total of 19 organochlorine pesticides were investigated in ten subsamples of maize, ten subsamples of cowpea and nine subsamples of drinking water. Analytical methods included solvent extraction of the pesticide residues and their subsequent quantification using gas chromatography-mass spectrometry (GC/MS). Estimated daily intakes (EDIs) of pesticides were also determined. Pesticides residues in drinking water (0.04–0.40 µg l^?1) were higher than the maximum residue limit (MRL) (0.03 µg l^?1) set by the World Health Organization (WHO). Dieldrin, endrin, heptachlor epoxide and endosulfan levels (13.16–98.79 µg kg^?1) in cowpea grains exceeded MRLs applied in France (10–50 µg kg^?1). Contaminants’ levels in maize grains (0.53–65.70 µg kg^?1) were below the MRLs (20–100 µg kg^?1) set by the Food and Agriculture Organization (FAO) and the WHO. EDIs of the tested pesticides ranged from 0.02% to 162.07% of the acceptable daily intakes (ADIs). Population exposure levels of dieldrin and heptachlor epoxide were higher than the FAO/WHO standards. A comprehensive national monitoring programme on organochlorine pesticides should be undertaken to include such other relevant sources like meat, fish, eggs and milk.     

Genotype × environment influence on cowpea (Vigna unguiculata (L) walp) antinutritional factors: 1 – trypsin inhibitors,tannins, phytic acid and haemagglutinin

The relative influence of genotype, environment and genotype×environment effects on four antinutritional factors (g kg⁻¹) of importance in cowpea were studied using 15 local and improved cowpea genotypes grown in 12 environments, comprising three locations over four seasons per location. The locations Ago‐Iwoye (6°58′N4°00′E), Mokwa (9°17′N5°04E) and Kano (12°00′N8°31′E) were representatives of the major agroecological zones where cowpeas are produced. Genotypes effects were strongest in controlling trypsin inhibitor content, while the environment was the major source of variation for tannins, haemagglutinin and phytic acid contents. Thus, the variability in the levels of these antinutritional factors in cowpea seeds depends largely on the environment where they are grown. This implies that a cowpea genotype grown and consumed safely in an environment can be poisonous when grown and consumed in another environment. Genotype×environment effects were significant for tannins, haemagglutinins and trypsin inhibitor contents. Correlation coefficients (pooled data) from the three locations indicated that trypsin inhibitor was positively correlated to phytic acid (r=0.59, 0.001<P<0.05) and haemagglutinins (r=0.64, 0.001<P<0.05) but negatively correlated to tannin contents ( r=−0.79, 0.001<P<0.05). © 1999 Society of Chemical Industry     

Determination of phthalates in raw bovine milk by gas chromatography/time-of-flight mass spectrometry (GC/TOF-MS) and dietary intakes

Low levels of phthalates, including di(2-ethylhexyl) phthalate (DEHP), in raw bovine milk were determined using gas chromatography/time-of-flight mass spectrometry (GC/TOF-MS). A fast and convenient process of sample treatment combined with TOF-MS analysis (medium resolution >5000), yielded good recoveries (85–125%) and low limits of detection (<0.002 mg kg^?1). The most commonly used phthalate, DEHP, was found in 15 out of 30 samples monitored in this study. DEHP concentrations in raw milk ranged from not detected to 0.154 mg kg^?1, and the mean concentration was 0.057 mg kg^?1. The dietary intake of DEHP was about 0.004 mg kg^?1 body weight day^?1 if a child (24 months, 13 kg body weight) drinks 1 L day^?1 of milk that contains the mean concentration of DEHP found in raw milk. The estimated dietary intake corresponded to 8% of the European Union tolerable daily intake (TDI) of 0.05 mg kg^?1 body weight day^?1. Dimethyl phthalate (DMP) and di-n-butyl phthalate (DBP) were found from two and 20 samples, respectively, at low levels. Diethyl phthalate (DEP), butylbenzyl phthalate (BBP), and di-n-octyl phthalate (DnOP) were not found in any of the samples.     

COD (GADUS MORHUA) TRYPSIN HEAT INACTIVATION: A REACTION KINETICS STUDY

The heat inactivation of cod (Gadus morhua) trypsin was examined at 40–55C by nonlinear regression (NLR) analysis according to 1st-order, n-th order, or consecutive reaction kinetics. At 40C Cod trypsin was inactivated by a 2nd-order reaction; n = 2 (±0.014) with a pseudo rate constant (k′) of 6.46 (±0.04) × 10^?4 (s^?1). The order of reaction decreased with increasing temperature; n = 1.54 (±0.003) at 45C, n = 0.8 (±0.005) at 50C or n = 0.64 (±0.014) at 55C. At 45–55C the consecutive model also indicated 1st-order inactivation kinetics. SDS-PAGE analysis showed that with progressive heating the concentration of cod trypsin decreased and there was an appearance of lower molecular weight polypeptides. The results are consistent with a heat inactivation process involving trypsin autolysis. A mechanism for cod trypsin heat inactivation is proposed which accounts for the observed 1st-order or 2nd-order reaction kinetics as limiting cases.