Kinetics of Thiamin Degradation in Solutions under Ambient Storage Conditions

Thiamin is being incorporated into a variety of nutritionally enhanced beverages. Although thiamin degradation during thermal processing has been extensively studied, minimal data exist regarding its stability in solution during ambient storage. This study collected kinetic data for thiamin degradation in solutions as a function of pH, buffer type, and buffer concentration at 25 °C. Thiamin was incorporated into sodium phosphate and citrate buffer solutions, each prepared at 0.02 and 0.1 M and pH 4, 5, 6, and 7. Experimental solutions were stored in an incubator at 25 °C. Thiamin concentrations were analyzed at 9 time points over a 42‐wk period. Thiamin degradation data were modeled using pseudo‐1st‐order kinetics. Thiamin stability generally decreased as pH and buffer concentration increased in both phosphate and citrate buffers. In 0.1 M phosphate buffer, the time for a 10% loss of thiamin decreased from 79 wk at pH 4 to 3 wk at pH 7. At pH 6 and 7, thiamin stability was greater in citrate buffer than in phosphate buffer. However, at pH 4 and 5, thiamin stability was greater in phosphate buffer than citrate buffer. To optimize thiamin stability in low pH beverages, phosphate buffer would be more appropriate to use than citrate buffer, whereas citrate buffer should be used for better thiamin stability in high pH beverages.     

Kinetics of Protein Quality Loss in Enriched Pasta Stored in a Sine Wave Temperature Condition

The rate of loss of protein quality in enriched pasta was studied at constant temperature (30, 37 and 45°C) and under a continuous sine wave temperature fluctuation (25/45°C with a 24-hr period). Both loss of lysine by the fluoro-dinitro benzene (FDNB) method and a bioassay (Tetrahymena thermophila growth) for protein quality were employed. Significant loss of protein quality occurs in about 1 yr at temperatures above 30°C. The bioassay method showed that nutrient losses other than lysine could be occurring. Data from the constant temperature studies were used to predict the losses that occurred for the sine wave condition using the Hicks-Schwimmer model as modified with an Arrhenius approach. The prediction model gave about 15% error in comparison to actual losses. In addition, the rate of loss for the sine wave (25/45°C) was greater as predicted than the rate of loss at a constant mean temperature of 35°C.     

Evaluation of a Modified AOAC Determination for Thiamin and Riboflavin in Foods

Modifications of the AOAC thiamin and riboflavin methods allow determination of the two vitamins from aliquots of a single food sample with alternatives to obsolete or dangerous reagents. Mylase 100, an α-amylase enzyme which hydrolyzes thiamin esters, was shown to be effective at releasing thiamin in 3 hr over a pH range of 3.5–5.5, at 35 and 42°C. In thiochrome extraction, anhydrous isopropanol can be substituted for isobutanol, a suspected carcinogen.     

Thiamin, Riboflavin and Niacin Retention in Cooked Cowpeas as Affected by Kanwa Treatment

Retention of three water soluble B-vitamins in dry cowpeas cooked with a local tenderizer, named “kanwa,” were investigated. Results showed cooking (100°C) in kanwa or sodium bicarbonate decreased levels and retention of vitamins compared to controls cooked in water. Levels of vitamins in kanwa-cooked cowpeas were not significantly different from those in NaHCO₃ cooked samples. Retention in the alkaline cooking processes ranged 15–20% (thiamin), 26–49% (niacin) & 53–64% (riboflavin). Soaking followed by boiling at 100°C or pressure cooking (121°C) increased levels and retention of vitamins.     

Kinetics of Browning and Protein Quality Loss in Whey Powders During Steady State and Nonsteady State Storage Conditions

Comparison was made between the amount of browning and protein quality loss during storage of whey powder under steady state conditions (25, 35 and 45°C and a_w's of 0.33, 0.44 and 0.65 at each temperature) and a fluctuating temperature condition of 25/45°C with alternating 5 day periods at each temperature. The results showed that the maximum rate of browning and loss of protein quality (e-DNP-lysine and RNV by Tetrahymena assay) occured at a_w 0.44 rather than at a higher a_w as is found for many dried foods. The Q₁₀'s for the reactions were about 5 and 3.7 respectively, for browning and protein quality loss. Of major importance was that storage losses at constant a_w, but under the fluctuating temperature condition, were significantly greater than at the mean temperature of 35°C. Using steady state data from the 25, 35 and 45°C conditions, the prediction of browning and protein quality losses for the fluctuating condition compared favorably (+ 10%) to actual losses, based on the simple Arrhenius relationship which indicates that temperature history does not significantly change reaction mechanisms.     

Effect of Further Processing and Storage of Mechanically Deboned Chicken on Proximate Composition, Thiamin, Riboflavin and TBA Values

Mechanically deboned chicken (MDC), and its further processed products, frankfurters (FK) and bolognas (BG), were evaluated for proximate composition, thiamin, riboflavin and TBA values following processing and storage. Vitamin concentrations were found stable in MDC stored at 2°C for 2 days or at – 18°C for 180 days. The processing of FK and BG reduced the vitamin levels by0–12% on a dry weight basis. Storage of FK and BG for 42 days at 2°C or 180 days at – 18°C had no measurable effect on vitamin content. TBA values were generally low except their increases were significant in the salted MDC held at – 18°C. Proximate composition varied among products but was not affected by storage time and temperature.     

Influence of Initial Riboflavin Content on Retention in Pasta During Photodegradation and Cooking

Samples of enriched pasta were stored under controlled lighting conditions and the loss of riboflavin was determined. After an initial rapid degradation, the riboflavin level continued to decrease slowly. After 12 wk, more than 80% the riboflavin had degraded. When pasta samples- with varied levels of riboflavin enrichment were exposed to light for 2 days, riboflavin losses ranged from 57.8–64.3%. Riboflavin leaching from pasta during cooking was also shown to be concentration independent with 34.5–37.6% of the riboflavin solubilized in the cooking water. Riboflavin in pasta which had been exposed to light for 2 days prior to cooking had a similar percentage of the undegraded riboflavin leached into the cooking water.     

Simultaneous Determination of Thiamin and Riboflavin in Selected Foods by High-Performance Liquid Chromatography

A high-performance liquid chromatographic (HPLC) system that makes it possible to accurately and simultaneously quantitate low levels of riboflavin and thiamin (thiochrome) from single extracts following oxidation and sample preconcentration steps is described. Several food matrices were analyzed and the results compared to the AOAC method now in use. Within the range of standard deviations, both methods gave comparable values. This method is rapid, accurate, sensitive and economical, making it attractive to those who require routine analysis of thiamin and riboflavin.     

Effect of Adjusting the Water Activity to 0.95 with Different Solutes on the Kinetics of Thiamin Loss in a Model System

The kinetics of thiamin degradation in a model system of pH 6.0 and water activity (a_w) 0.95 controlled with NaCl, KC1, glycerol or Na₂SO₄, was studied. The type of solute used to adjust a_w, had a dramatic influence on the rate of degradation of thiamin. The loss of vitamin increased in the following order: NaCl > KCl > glycerol > Na₂SO₄. Activation energies, however, were independent of the type of solute and ranged between24–28 kcallmole.     

Inactivation Kinetics of Peach Pulp Pectin Methylesterase as a Function of High Hydrostatic Pressure and Temperature Process Conditions

A kinetic study of the inactivation of endogenous pectin methylesterase (PME) in Greek commercial peach pulp under high hydrostatic pressure (HHP; 100–800 MPa) combined with moderate temperature (30–70 °C) was conducted. Thermal inactivation of the enzyme at ambient pressure conditions was also studied. PME inactivation was modeled by first order kinetics at all conditions tested. High pressure and temperature acted synergistically on PME inactivation, except at the high temperature of 70 °C at the middle pressure range (100–600 MPa), where an antagonistic effect of pressure and temperature was observed. At this specific middle pressure range, an increase of pressure processing led to increased inactivation rate constants of peach PME. A multiparameter model was developed to express the PME inactivation rate constant as a function of temperature and pressure process conditions, taking into account the dependence of both activation energy and activation volume on pressure and temperature, respectively. A good correlation between experimental and predicted values of inactivation rate constants was established. This modeling approach enables the quantitative estimation of the HHP–temperature conditions needed to achieve a targeted PME inactivation in the peach pulp.     

Thiamin, Riboflavin and α-Tocopherol Retention in Processed and Stored Irradiated Pork

Combination treatments for preservation of irradiated pork were investigated with respect to vitamin loss. Ground pork was prepared under nitrogen and packaged in anaerobic foil. The samples were enzyme denatured by heating before and after irradiation, then cooked and stored. Irradiation resulted in thiamin loss, but neither riboflavin nor α-tocopherol was affected. Neither thiamin nor riboflavin was affected by heat denaturation, cooking or storage, but heating and cooking increased the measured α-tocopherol. The lack of loss of the vitamins was attributed to the exclusion of oxygen.     

Gamma Irradiation Effects on Thiamin and Riboflavin in Beef, Lamb, Pork, and Turkey

A study was made of the loss of thiamin and riboflavin due to gamma irradiation of beef, lamb and pork longissimus dorsi, turkey breast and leg muscles. Thiamin losses averaged 11%/kiloGray (kGy) and riboflavin losses 2.5%kGy above three kGy. The rate of loss of thiamin in beef was higher than that in lamb, pork and turkey leg, but not turkey breast. with losses of 16%/kGy in beef and 8%/kGy in lamb. The rate of thiamin loss was not related to sulfhydryl, protein, moisture, fat or water content, pH or reducing capacity by redox titration. Loss of riboflavin was not different among species. Any detriment from such slight losses would seem to be more than compensated by the advantage of controlling bacteriological contamination by irradiation processing.     

Kinetics of Oxidation of Potato Chips under Constant Temperature and Sine Wave Temperature Conditions

Lipid oxidation in potato chips at 30, 37 and 45°C followed zero order kinetics as measured by peroxide value (PV). An Arrhenius plot of log k versus (T°K)-^?1 snowed slight underprediction at low temperatures. Data from constant conditions were used to predict the extent of this free radical reaction under a sine wave temperature fluctuation (25/45°C with a 24 hr period). Predictions of effective rate constant, temperature and extent were found to agree to within 3.5% of the actual results up to a PV of 7 where bimolecular oxidation occurred. The sine wave condition entered the bimolecular oxidation sooner than was observed under steady data for the same effective temperature.     

低温贮藏条件下创伤弧菌和副溶血性弧菌失活模型的建立

为掌握对虾中创伤弧菌和副溶血性弧菌在5℃和一18~C低温贮藏条件下失活动力学特征,分别采用线性模型、Weibull模型、Logistic模型对创伤弧菌和副溶血性弧菌的失活曲线进行拟合。研究结果表明,在5~C条件下,创伤弧茵VvHB09的耐冷力较强;．18℃条件下,副溶血性弧菌ATCC17802和创伤弧菌VvSH09的耐冷力较强。线性模型比weibull模型、Logistic模型更适合拟合创伤弧菌和副溶血性弧菌的失活特征。     

Degradation Kinetics of Chlorophyll in Peas as a Function of pH

The kinetics of chlorophyll degradation in pea puree were determined in a specially designed reactor with on‐line pH control capability. Without pH control, the pH of the pea puree decreased continuously with heating due to acid formation; the pH was maintained within ±0.1 of the desired value with on‐line pH control. Chlorophyll (both a and b) degradation followed the first‐order reaction model. The temperature dependence of the rate constant was adequately modeled by the Arrhenius equation. The activation energy was independent of pH and was 17.5 kcal/mol and 17 kcal/mol for chlorophyll a and chlorophyll b, respectively. The degradation rate constant decreased log‐linearly as the pH was increased. A mathematical model was developed to predict the chlorophyll concentrations as a function of time, temperature and pH.     

Thiamin, Riboflavin, and Nicotinic Acid Contents of Tropical Root Crops from the South Pacific

The thiamin, riboflavin, and nicotinic acid contents of sweet potato (Ipomea batatas, taro (Colocasia esculenta), giant taro (Alocasia macrorrhiza), giant swamp taro (Cyrtosperma chamissonis), taro (Xan-thosoma spp), yam (Dioscorea alata and D. esculenta) were determined for fresh and 40°C dried material obtained from six South Pacific countries. Losses on drying at 40°C for 2-3 days were 10-15% for the three vitamins. Sweet potato contained the largest amount of thiamin (40-120 μg/100g fresh weight) and along with Colocasia esculenta and Xanthosoma spp. the largest amounts of nicotinic acid. The root crops provided inadequate amounts of thiamin, riboflavin, and nicotinic acid with values ranging from 12-123, 12-59 and 220-1310 Hg/100g fresh weight, respectively. Losses on cooking were about the same for all vitamins and root crops, with about a 20% loss on boiling (water retained) or baking and about a 40% loss on boiling (water discarded).     

Stability of α-Tocopherol, Thiamin, Riboflavin and Retinol in Pork Muscle and Liver during Heating as Affected by Dietary Supplementation

The α-tocopherol (Vit E) and ascorbic acid (Vit C) supplementation of pig diets increased (P<0.05) liver α-tocopherol concentrations. After heating, the liver samples of both treated groups and the longissimus dorsi muscle samples of the vitamin C group showed increased riboflavin retention (P<0.05). The supplemented and control groups did not show differences regarding retention of α-tocopherol, retinol and thiamin in heated liver and longissimus dorsi. Dietary vitamin C resulted in higher liver vitamin E and was most effective in protecting riboflavin against loss during heating of liver or longissimus dorsi.