Stability Of Thiamine Research Articles

Effect of UV radiation, temperature, acid, and basic solutions on the chemical stability of thiamine

Thiamine, a water-soluble vitamin termed vitamin B1, is found in several pharmaceutical and nutritional products. In this study, the standard aqueous solution of thiamine was exposed to a variety of circumstances, including UV radiation for 5, 10, 15, 20, 30, and 40 minutes, temperatures of 20, 25, 30, 35, 40, and 45 °C, and concentrations of 1%, 5%, and 10% hydrochloric acid and sodium hydroxide. Its degradation is being examined with a UV spectrophotometer. Thiamine is UV-sensitive after 5 minutes, has a slight effect at temperatures up to 45 °C, and is unstable at different acid and basic concentrations. Such methods can be used to investigate the stress-induced degradation of thiamine.

Stability and Requirement for Thiamin in a Cell Culture Feed Used to Produce New Biological Entities.

Thiamin is susceptible to heat and oxidation, which is a concern for the development of concentrated and room temperature stable feeds used to produce recombinant proteins. Hence, it is critical to understand the reactivity and necessity of the vitamin in liquid feeds to be able to either develop mitigation strategies to stabilize the vitamin or to remove thiamin from formulations if it is unnecessary. LC-MS/MS was used to investigate thiamin stability in different liquid feed formulations and to identify thiamin degradation products. Results indicate oxidation of thiamin and interaction with amino acids, keto acids, and sulfur containing components. Thiamin necessity in feed was assessed during a fed batch experiment, focusing on cell performance and critical quality attributes of the produced recombinant proteins. The impact of thiamin depletion in the feed on the intra- and extracellular metabolome was investigated using untargeted LC-MS/MS. Results indicate that thiamin can be removed from the feed without affecting the performance or the intra- and extracellular metabolome of the tested cell lines. Overall, profound insights on thiamin reactivity and necessity are presented in this study, suggesting the removal of the dispensable and instable vitamin as a simple means for the development of next generation feeds used to produce therapeutic biological entities.

Impacts of vitamin premix and/or yeast ingredient inclusion in a canned cat food on thiamin retention during 6 months of storage.

Low thiamin levels in thermally processed canned cat foods are concerning for the pet food industry. However, there is little information on storage stability of thiamin in this food format or if inclusion of select ingredients, such as dried yeasts, has an effect. Therefore, the objective was to evaluate the storage stability of thiamin when a vitamin premix and/or yeasts ingredients were included in a canned cat food. The factorial treatment arrangement consisted of 2 levels of vitamin premix (with or without) and 4 inclusions of yeast (NY = none, LBV = Lalmin B Complex Vitamins, BY = product #1064B, or EA = BGYADVANTAGE). Diets were stored for 6 months and analyzed every month for thiamin. Data were analyzed as a mixed model (SAS v. 9.4; SAS Institute, Cary, NC) with fixed effects (vitamin premix, yeast, time, and their two-way and three-way interactions) and random effects (production day and the interaction of production day, vitamin premix, and yeast). Significance was set at P < 0.05 and Fisher's LSD was used to separate means. Diets including the vitamin premix [average 55.1 mg/kg dry matter basis (DMB)] contained more (P < 0.05) thiamin than diets that did not (average 7.5 mg/kg DMB). Inclusion of LBV (average 40.3 mg/kg DMB) resulted in the highest (P < 0.05) levels of thiamin, followed by BY (P < 0.05; average 26.9 mg/kg DMB). Diets with NY and EA contained the lowest (P < 0.05) levels of thiamin and were not different from each other (P > 0.05; average 19.3 mg/kg DMB). The diet containing vitamin premix without yeast lost (P < 0.05) 17.8% thiamin while diets containing a yeast ingredient maintained thiamin levels better during storage. This suggested that thiamin from yeast ingredients was more resistant to degradation during storage and should be considered when designing new canned cat foods.

Human health benefits from buckwheat nutrients

Buckwheat contains a variety of nutrients in its grains. The main compounds are proteins, rutin, polysacchardes, dietary fibre, lipids, polyphenols and micronutrients (minerals and vitamins). The total content of these components depends on different factors, such as the species and the environment. The amino acid composition of buckwheat proteins is well balanced and of a high biological value, although the protein digestibility is relatively low. Buckwheat grains are an important source of microelements, such as: Zn, Cu, Mn, Se, and macro elements: K, Na, Ca, and Mg. With 80% unsaturated fatty acids more than 40% are constituted by polyunsaturated fatty acid (PUFA). The significant contents of rutin, catechins and other polyphenols as well as their potential antioxidant activity are also of significance to the dietary value. Moreover, buckwheat grains are a rich source of TDF (total dietary fibre), soluble dietary fibre (SDF), and are applied in the prevention of obesity and diabetes. An increasing incidence of allergy manifestations or symptoms is observed in people who consume buckwheat-containing food products often and in high quantities. The main reason for such immunological disorders is low molecular weight proteins, particularly those with molecular weights of 15, 22, or 26 kDa. These are concentrated in the peripheral parts of endosperm and embryo, hence the highest quantity of B vitamins is found in the bran. Tartary buckwheat bran contains about 6% of daily therapeutic doses of pyridoxine, effective in the reduction of blood plasma homocysteine levels. Protein extracts are more efficient in lowering the blood cholesterol level, particularly that of LDL and VLDL. Buckwheat proteins products (BWP) are acknowledged as preventive nutrients. They use advisable modifications, e.g. enzymatic modifications that consist in enzymatic separation of allergenic constituents or controlled fermentations performed by yeast or mould strains. Vitamins are a group of organic compounds that are essential in very small amounts for the normal functioning of the human body. They vary widely in their chemical and physiological functions and are broadly distributed in natural food sources. Buckwheat grains contain higher levels of vitamin B1 (thiamine), B2 (riboflavin), E (tocopherol) and B3 (niacin and niacinamide) compared with most cereals. Generally, tartary buckwheat has more vitamin B1, B2 and B3, but less vitamin E than common buckwheat. In general, tartary buck wheat has higher levels of vitamin B than common buck-wheat. Thiamine-binding proteins can improve the stability of thiamine during storage and improve the bioavailability of thiamine. Levels of vitamin C and the sum of vitamin B1and B6 can be increased by germinating buckwheat. The level of vitamin C can be increased by up to 0·25mg/g in buckwheat sprouts. Wheat, barley, oat, rye and buckwheat groats exhibit the same maximum level of tocopherols, with γ-tocopherol being the main one.

115 Stability of Thiamine Supplied by Vitamin Premix and Yeast Ingredients in Canned Cat Food

Abstract Despite numerous process modifications, thiamine retention of canned cat food has not improved. Yeasts possess a binding protein which may provide a thiamine form able to withstand retort processing. Therefore, the objective was to evaluate dried yeasts as thiamine sources in canned cat food. Treatments were arranged as a 2ｘ4 factorial with 2 levels of vitamin premix (with or without) and 4 sources of yeast (none (NY), LBV, BY, or EA). Inclusion of LBV matched the thiamine contribution from the vitamin premix and BY and EA were capped at 5%. Three replicates were processed in a horizontal still retort to an average total F0 of 79.23 minutes. Thiamine degradation was calculated as the difference between pre- and post-retort thiamine contents. Data were analyzed as a randomized complete block design with pre-retort thiamine content as a covariate and production day as a random effect. The Fisher’s LSD post hoc comparison test was performed with ⍺ = 0.05. On average, experimental formulas retained 33.75% thiamine. Thiamine degradation was not affected by the inclusion of vitamin premix (P = 0.0670), but was affected by the inclusion of yeast (P = 0.0232) and the interaction between vitamin premix and yeast (P = 0.0002). Thiamine loss between NY (-31.3 mg/kg DM) and BY (-33.8 mg/kg DM) were similar (P &amp;gt; 0.05) whereas EA (-40.5 mg/kg DM) and LBV (-55.6 mg/kg DM) lost more (P &amp;lt; 0.05) thiamine than NY. The treatment of EA with vitamin premix (-70.3 mg/kg DM) lost more (P &amp;lt; 0.05) thiamine than no yeast, BY, or EA without vitamin premix (average -17.4 mg/kg DM) and all others (average -57.3 mg/kg DM) were intermediate (P &amp;gt; 0.05). Inclusion of vitamin premix with yeast did not minimize thiamine loss and BY exhibited similar thiamine degradation as intrinsic thiamine in standard ingredients.

Thiamine in Lipid Systems vs. the Antioxidant Activity of Epigallocatechin Gallate and Caffeine

The aim of this study was to determine correlations between the concentration of thiamine hydrochloride or thiamine pyrophosphate and the antioxidant activity of epigallocatechin gallate (EGCG) and caffeine, as well as thiamine stability. The study was conducted in model systems. Oxidation degree indices of soybean oil (peroxide value and anisidine value LAN) and concentrations of total thiamine were determined. To compare the dynamics of the changes in thiamine content during storage, half-life T1/2 was determined. There was a strong correlation between the stability of thiamine and the stability of the oil. Thiamine was particularly sensitive to secondary oxidation products. Higher losses of thiamine introduced in the form of thiamine pyrophosphate were found (4–6%). The addition of tea components increased fat stability and thus reduced thiamine losses. The dynamics of thiamine loss were found to be lower with EGCG than caffeine. The antioxidant activity of these components was significantly reduced when the content of thiamine (1.0–20.0 mg/100 g) was higher than the natural level in foods. In order to maintain thiamine stability and the high activity of the active tea ingredients, it is necessary to consider their simultaneous addition to the systems in concentrations that limit their interactions.

Amorphization of Thiamine Mononitrate: A Study of Crystallization Inhibition and Chemical Stability of Thiamine in Thiamine Mononitrate Amorphous Solid Dispersions

This study investigated thiamine degradation in thiamine mononitrate (TMN):polymer solid dispersions, accounting for the physical state of the vitamin and the recrystallization tendency of TMN in these dispersions. Results were compared with those from solid dispersions containing a different salt form of thiamine (thiamine chloride hydrochloride (TClHCl)). TMN:polymer dispersions were prepared by lyophilizing solutions containing TMN and amorphous polymers (pectin and PVP (polyvinylpyrrolidone)). Samples were stored in controlled temperature and relative humidity (RH) environments for eight weeks and monitored periodically by X-ray diffraction and high performance liquid chromatography (HPLC). Moisture sorption, glass transition temperature (Tg), intermolecular interactions, and pH were also determined. Similar to the TClHCl:polymer dispersions, thiamine was more chemically labile in the amorphous state than the crystalline state, when present in lower proportions in amorphous TMN:polymer dispersions despite increasing Tg values, when environmental storage conditions exceeded the Tg of the dispersion, and when co-formulated with PVP compared to pectin. When thiamine remained as an amorphous solid, chemical stability of thiamine did not differ as a function of counterion present (TMN vs. TClHCl). However, storage at 75% RH led to hydration of thiamine:PVP dispersions, and the resulting pH of the solutions as a function of thiamine salt form led to a higher chemical stability in the acidic TClHCl samples than in the neutral TMN samples.

Amorphization of Thiamine Chloride Hydrochloride: Effects of Physical State and Polymer Type on the Chemical Stability of Thiamine in Solid Dispersions.

Thiamine is an essential micronutrient, but delivery of the vitamin in supplements or foods is challenging because it is unstable under heat, alkaline pH, and processing/storage conditions. Although distributed as a crystalline ingredient, thiamine chloride hydrochloride (TClHCl) likely exists in the amorphous state, specifically in supplements. Amorphous solids are generally less chemically stable than their crystalline counterparts, which is an unexplored area related to thiamine delivery. The objective of this study was to document thiamine degradation in the amorphous state. TClHCl:polymer dispersions were prepared by lyophilizing solutions containing TClHCl and amorphous polymers (pectin and PVP (poly[vinylpyrrolidone])). Samples were stored in controlled temperature (30–60 °C) and relative humidity (11%) environments for 8 weeks and monitored periodically by X-ray diffraction (to document physical state) and HPLC (to quantify degradation). Moisture sorption, glass transition temperature (Tg), intermolecular interactions, and pH were also determined. Thiamine was more labile in the amorphous state than the crystalline state and when present in lower proportions in amorphous polymer dispersions, despite increasing Tg values. Thiamine was more stable in pectin dispersions than PVP dispersions, attributed to differences in presence and extent of intermolecular interactions between TClHCl and pectin. The results of this study can be used to control thiamine degradation in food products and supplements to improve thiamine delivery and decrease rate of deficiency.

Stability of high-dose thiamine in parenteral nutrition for treatment of patients with Wernicke's encephalopathy.

Wernicke's encephalopathy is associated mainly with malnourishment in alcohol-dependent patients but can be caused also by cancer, Crohn's disease, gastrointestinal surgery or prolonged parenteral nutrition (PN) without adequate supplementation of vitamins. The disorder, with a significant mortality rate of up to 20%, is often associated with the underlying disease and intensifies after administration of non-supplemented PN. Thus, it seems justified to add thiamine to PN admixtures prepared for parenterally fed patients. Due to the lack of data on the stability of thiamine in PN admixtures at concentrations exceeding 60mg/L, we decided to determine the possibility of adding a high dose of thiamine (800mg per bag, 320mg/L) to PN admixtures in order to treat Wernicke's encephalopathy in malnourished patients. The study aimed to assess the stability of the physical properties of PN admixtures (pH, zeta potential, particle size) and to determine thiamine content using an HPLC method. Thiamine was found to degrade regardless of the PN admixture composition and storage conditions. The highest decrease in thiamine content was observed at room temperature without light protection whereas the lowest at a temperature of 4±1°C with light protection. The treatment of Wernicke's encephalopathy in parenterally fed patients is possible with the use of high thiamine doses (800mg) added to PN admixtures without a decrease in the drug content above 10% within the first 24h. It should be emphasized that thiamine as a photosensitive drug must be stored and administered under conditions ensuring light protection.

Validation of a HPLC Method for Quantification of Thiamine and Its Phosphate Esters in Rat Brain Tissue

The present data show a fast and efficient biological sample processing method for the extraction of thiamine (vitamin B1) and its mono-(TMP) and di-(TDP) phosphate esters from hippocampus, thalamus and prefrontal cortex (PFC) and blood sample of the rodents. In addition, using the hippocampus and standards of these three compounds we validated an isocratic fluorescence HPLC procedure for a simultaneous detection of them in a single chromatogram within a total run time of about 12 min. Reproducibility for TDP, TMP and B1 was 2.66%, 4.50% and 7.43% (intraday) and 37.54%, 25.39% and 25.87% (interday), respectively. Recovery assays were between 96.0% and 101.7%. The calibration curves were linear and the concentrations of the three compounds, all in nanomolar range, were determined in the brain areas and in the blood samples. When compared to the current methods in the literature, this new method provides information on essential variables, such as linearity range and limit of detection, reproducibility and stability of thiamine, TMP and TDP in rat brain samples. The present data on sample processing and B1 and its phosphate ester level determinations are the first to be validated using hippocampus samples of rats.

Effect of cooking methods on the stability of thiamin and folic acid in fortified rice

Rice fortification offers great potential to deliver essential micronutrients to a large part of the world population. However, high temperatures required for cooking rice are deleterious to thermally labile micronutrients. This study evaluated the content and stability of thiamin and folic acid in fortified rice after different cooking methods (stir-frying, boiling, cooking in a microwave oven and boiling in a Food Service). The analyses were performed by High Performance Liquid Chromatography (HPLC). The fortified rice showed the highest thiamin content (0.97 mg/kg) and retention (65.4%) when cooked in microwave oven, and for folic acid the lowest content (0.17 mg/kg) and the highest retention (96.11%) when cooked in a Food Service and stir-fried, respectively. In conclusion, the stability of thiamin and folic acid varied according to the cooking method and the stability of folic acid presented higher percentages in relation to thiamin in the different methods.

Thiamine losses during storage of pasteurised and sterilized model systems of minced chicken meat with addition of fresh and oxidized fat, and antioxidants

The aim of the study was to determine the effect of pasteurisation and sterilization of model systems of minced chicken meat in the presence of low or high-oxidised pork lard, soy and sunflower oil, as well as casein hydrolysate and rosemary extract, on losses of thiamine in model systems. In the samples, the thiamine content was analysed periodically by thiochromium method, as well as rate of lipid oxidation based on measurement of peroxide value (PV) by iodometric method and p-anisidine value (AV) by spectrophotometric method. It was observed that the thiamine losses in model systems of minced chicken after pasteurisation (61-71%) were higher than after sterilization (57-67%). Introduction of high-oxidised fat increased the total thiamine losses both during thermal processing and storage of meat samples (to 23%). A strong relationship was established between thiamine losses and rate of fat oxidation. The lowest total thiamine losses were observed in the samples with low-oxidised pork lard. Antioxidant addition (rosemary extract or casein hydrolysate) into meat samples limited the thiamine losses. However, the effect depended on oxidation of fat that was mixed with meat. In the samples with low-oxidised fat, higher protective effect was found for rosemary extract (7-11%). In the samples with high-oxidised fat, casein hydrolysate was superior to rosemary extract (14%). In order to increase the stability of thiamine in pasteurized or sterilized meat products with fats, the influence of fat type and its oxidative stability should be taken under consideration. Moreover, the addition of rosemary extract or casein hydrolysate has impact on the thiamine losses since it slows down lipid oxidation to a significant extent.

Hydrolytic destruction of thiamine, especially in the presence of cyanocobalamin.

Abstract The hydrolytic destruction of thiamine hydrochloride in various buffer solutions at pH 4.5 at 100° has been investigated. The rate of hydrolysis approximated to that of a first order reaction, the salts of weak organic acids acting as catalysts so that buffer salts could not retard the decomposition. It was confirmed that the hydrolytic products of thiamine affect the stability of cyanocobalamin, and that low concentrations of ferric ions can protect cyanocobalamin against the effects of thiamine breakdown products, but this occurs without appreciably affecting the stability of thiamine itself.

Changes in vitamin content of powder enteral formulas as a consequence of storage

Abstract The thiamine, vitamin E (α-, γ- and δ-tocopherol) and vitamin A (all- trans and 13- cis -retinol) contents of four commercial powder enteral formulas (A, B, C and D) have been determined. The vitamin intake provided by the studied formulas was always above the US daily recommendations. Powder enteral formulas A and D were stored at 30 °C for up to 6 months with a water activity of 0.44 ( A w = 0.44), and formula A was also stored under atmospheric conditions for 3, 4 and 6 months. Formulas A and D kept at 30 °C and A w = 0.44 suffered a gradual loss in vitamin content (from 3% to 4% after 1 month to 58–60% after 6 months). Formula A, stored at 30 °C under atmospheric conditions, underwent a slight reduction in vitamin content after 3 months, similar to that found after 1 month with A w = 0.44, and from that time onward, this decreased steadily (to 30% after 6 months). The RDA of thiamine, vitamin E and vitamin A for women and men were met only when the powder enteral formulas were stored at 30 °C with A w = 0.44 up to 1 month and without A w up to 3 months. These results show that A w and storage period have a marked effect on the stability of thiamine, vitamin E and A during the storage of powder enteral formulas and should be taken into consideration for the shelf-life of the product.

Stability of vitamin B1 in Ultra Rice® in the presence of encapsulated ferrous fumarate

Food fortification with iron is effective in combating iron-deficiency anemia. As iron is reactive, it can destroy micronutrients, contribute to poor taste, and discolor the food. Encapsulation could be used to prevent the reaction of iron with food components. The stability of thiamin (vitamin B1) and its effects on organoleptic properties in Ultra Rice® were investigated in the presence of encapsulated ferrous fumarate. The preparation of simulated rice grains did not affect the solubility of encapsulated ferrous fumarate in simulated gastric juice. After 20 weeks at 40°C/∼100% relative humidity, essentially all of the vitamin B1 and ferrous iron were retained. Antioxidants were effective in preventing the loss of thiamin and retarding oxidative rancidity catalyzed by ferrous iron. This study demonstrated the feasibility of incorporating both iron and vitamin B1 in a stable Ultra Rice® formulation. Inclusion of other stable B vitamins in the formulation should be also feasible.

The contribution of Asian noodles to dietary thiamine intakes: A study of commercial dried products

Cereal based foods, including Asian noodles which represent the end use of at least one-eighth of global wheat production, are potentially good sources of thiamine. However, there is a lack of data on the stability of thiamine during processing. The aim of this study was to investigate the thiamine contents of three styles of Asian noodle products: white salted, yellow alkaline and instant. A standard method of analysis (Association of Official Analytical Chemists (AOAC), method number 953.17) was used to determine the thiamine content of noodles before and after cooking. Factors influencing thiamine stability were also investigated. The results showed that Asian noodles include products which vary significantly in formulation and are manufactured by distinct processes. pH levels were highest in yellow alkaline and lowest in white salted style. White salted noodles have higher thiamine levels although there is clearly variation between individual samples for each style of product. For most samples, thiamine levels were relatively low and considerable losses occurred during cooking. Thiamine values were particularly low for samples where alkaline salts were incorporated during manufacture. It is concluded that greater losses occur where higher pH values were observed and there is considerable variation in the thiamine content of Asian noodles.

The impact of flours and product storage on the thiamin content of Asian noodles

Thiamin is essential for human health and wheat foods are generally considered to be a good source of thiamin. However, dietary levels may be limited because of losses during processing. The aim of this study was to investigate the level of thiamin in a variety of wheat flour products along with the factors impacting on the thiamin content of Asian noodles particularly during storage. A standard fluorometric procedure was selected for the determination of thiamin in flours and noodle samples. White salted, yellow alkaline and instant noodles were prepared and the impact of storage conditions on thiamin levels analysed. Noodle pH appeared to be directly related to the amount of alkaline salt added and this in turn influenced the thiamin stability. The losses varied between the different styles with the greatest decreases occurring in the fresh yellow alkaline noodles. Prolonged drying at 40 °C for up to 9 days had no adverse influence on the ultimate thiamin status of these products. Storage of dried noodles for up to 4 months did not result in any further loss of thiamin. It is concluded that the potential of Asian noodles to contribute to dietary thiamin intakes appears to be limited in those where alkaline salts are included in the formulation.

The influence of formulation and processing on stability of thiamin in three styles of Asian noodles

Asian styles of noodle products represent the end-use of at least one eighth of all wheat produced globally and are potentially a good dietary source of essential nutrients. In order to investigate the factors influencing thiamin content, three styles of noodles were made under controlled laboratory conditions. The losses during preparation of dried white salted noodles were low. Boiling of these noodles resulted in a 43% decline in total thiamin level. In contrast, the relative losses of thiamin were high for yellow alkaline noodles and these occurred at each step in the process including dough mixing and drying. For instant noodles decreases also occurred at each step and these were smaller than for yellow alkaline but greater than for white salted noodles. The variation in ingredients and processing accounts at least partially for differences in thiamin levels of different noodle styles.

Kinetics of Thiamin Degradation in Solutions under Ambient Storage Conditions

ABSTRACT: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.

Effect of Sample Handling on Thiamine and Thiaminolytic Activity in Alewife

AbstractAlewives Alosa pseudoharengus were collected to evaluate handling and processing conditions that may affect the measurement of their thiamine–thiaminase content. Fish were captured by otter trawl, and reference samples of live fish were quick‐frozen on dry ice immediately following capture. Other samples were placed on wet ice (4°C) or held in ambient lake water (21.5°C) for periods of up to 5 h before freezing. Total thiamine levels for reference samples averaged 26 nmol/g and consisted of 66, 15, and 19% thiamine pyrophosphate (TPP), thiamine monophosphate (TMP), and unphosphorylated thiamine (Th), respectively. After 120 min at either 4°C or 21.5°C, total thiamine concentrations were lower. At 21.5°C, the TPP proportion had decreased by 30 min and the proportion as Th increased after 60 min. In the groups sampled after 5 h, total thiamine concentrations were not altered but the proportion of TPP was lower and that of Th was higher than in reference samples. The stability of thiamine in thawed muscle samples from previously frozen alewives was poor (40% loss by 1 h at 22°C and 30% loss by 2 h at 4°C). Thiaminase activity averaged 5,975 pmol·g wet weight−1·min−1 in reference samples. In fresh‐caught alewives, thiaminase activities were remarkably consistent throughout the sampling period. At 4°C, thiaminase activity in muscle tissue from previously frozen alewives was stable for the entire investigation period. At 25°C, the activity initially increased by 40% after 60 min but then decreased to 50% of initial value after 5 h. We conclude that sampling times greater than 25 min could cause some changes in the various thiamine forms and net loss in total thiamine. The thiamine content in previously frozen alewife samples is highly labile, requiring low temperatures during processing for analysis.