Moisture sorption isotherms of sorghum malt at 40 and 50 °C

The desorption and adsorption equilibrium moisture isotherms of sorghum malt at the temperatures of 40 and 50 °C, over the water activity range of 0.1-0.9, were determined using the static gravimetric method. A non-linear regression programme was used to fit five moisture sorption isotherm models [Modified Henderson, Modified Chung-Pfost, Modified Guggenheim-Anderson-de Boer (GAB), Modified Halsey and Modified Oswin] to the experimental data. The models were compared using the standard error of estimate, mean relative percentage deviation, fraction explained variation and residual plots.The Modified Chung-Pfost model was found to be the best for predicting the desorption equilibrium moisture content, while the adsorption equilibrium moisture content was best predicted by the Modified Oswin model. The desorption and adsorption water activities were found to be best fitted by the Modified Oswin model.The moisture sorption isotherms were sigmoidal in shape and showed a marked effect of temperature. The span of the moisture sorption hysteresis loop formed, decreased with increase in temperature, while the size increased with increase in temperature.     

Effect of glucose on the stability of fresh mutton during storage at ambient temperature (25 ± 2 °C)

The feasibility of using d-glucose to extend the shelf life of fresh mutton at 25 ± 2 °C was investigated. Aqueous solutions of 5% d-glucose (w/v) containing 1000 ppm potassium sorbate, when applied on acidulant-treated mutton, are able to inhibit spoilage by delaying proteolytic activity, as seen by significantly lower (P < 0.01) levels of biogenic amines until 4 days of storage. Though there was no significant change in standard plate count during storage, as compared with a 1 day control, Enterobacteria were significantly (P < 0.01) inhibited. Cadaverine, the marker for threshold level of spoilage, was absent up to 4 days. Measurement of glucose retention revealed that 0.25% (0.25 g/100 g mutton) was still available at the end of 4 days, when no spoilage had set in, though there was a slight fermented odour. Thus, the investigation shows that, surface treatment with glucose helps to extend the shelf life of fresh mutton up to 3 days at 25 ± 2 °C.     

壳聚糖-单糖美拉德反应产物的制备及其在抗菌和抗氧化中的应用研究进展

为了对美拉德反应体系进行综合评价以及优化茶氨酸-葡萄糖美拉德反应条件,本研究构建了茶氨酸-葡萄糖美拉德反应综合评价值的人工神经网络耦联遗传算法（BP-GA）模型,优化得到了最佳反应条件。先通过熵值法求出荧光值、A₂₉₄、A₄₂₀、葡萄糖及茶氨酸剩余量五个评价指标之间的权重,再结合单因素实验及正交试验结果,建立输入为实验因素参数,输出为美拉德反应综合评价值的BP-GA人工神经网络模型,最后使用建立好的模型得到茶氨酸-葡萄糖美拉德反应的最优条件及相应的美拉德反应综合评价值。结果表明,通过建立的BP-GA模型进行全局优化得到茶氨酸-葡萄糖美拉德反应的最优条件为：反应温度117.6 ℃,反应时间1.8 h,pH7.3,羰基氨比1:2,此条件下美拉德反应的综合评价值为93.22。经过与正交试验得到的结果比较,发现BP-GA模型具有良好的预测性能。利用BP-GA模型,本研究得到了模型美拉德反应的最优条件,这将为美拉德反应模拟体系的构建及反应的预测提供参考。

     

Comparison of the effects of sucrose and hexose on furfural formation and browning in cookies baked at different temperatures

The influence of the type of sugar and baking temperature on sugar degradation, hydroxymethylfurfural (HMF) formation and browning was studied in model cookies. The baking process was characterised by the temperature in the cookie and the water content and activity. A reference browning was selected to compare the differently processed cookies. The accumulation of HMF was modelled at three temperatures for three formulas (sucrose (S-CK), glucose (G-CK) or fructose (F-CK)). HMF started to accumulate at a_w between 0.5 and 0.7 depending on the temperature and followed a first order kinetic, highly dependent on the baking temperature and type of sugar. Cookies baked at 200 °C accumulated 10–100 times less HMF than those baked at higher temperatures. Below 250 °C, S-CK produced less HMF than G- or F-CK, but the inverse was observed at 300 °C.     

Investigation of the formation of Strecker aldehydes from the reaction of Amadori rearrangement products with α-amino acids in low moisture model systems

 The formation of Strecker aldehydes in low moisture model systems (based on microcrystalline cellulose) containing the Amadori rearrangement product (ARP) fructose-leucine (Fru-Leu), the amino acid isoleucine (Ile) and the amine o-phenylenediamine (OPD) respectively in varying molar ratios was investigated. The model systems were heated under constant conditions and the formation of Strecker aldehydes analysed using headspace-GC. The experimental results obtained provide evidence that the formation of Strecker aldehydes does not only occur via ordinary Strecker degradation but also via alternative reaction pathways branching off directly from the ARP. Alternative reaction pathways are proposed. Received: 2 November 1999 / Revised version: 3 February 2000     

Preparation of red jujube powder with high content of Amadori compounds and higher antioxidant activity by controlling the Maillard reaction

Amadori compounds (ACs) are stable compounds produced in the early stage of the Maillard reaction (MR) with health benefits such as immunomodulatory, antithrombosis, and tumor-preventive effects. Jujube is a medicinal and edible fruit in China. It is rich in free amino acids and reducing sugar, but traditionally, little attention was paid to the formation of ACs when jujube was processed, neither the influence of ACs on health effects. In this paper, we aimed to increase ACs through controlling the MR during different heating processes of jujube powder with adjusted water content and find the most effective AC that contributed to the antioxidant effects of jujube powder. The optimal dry-heating conditions to produce ACs were as follows: The water activity was 0.294, the heating temperature was 90°C, and the time was 120 min. After processing, the ACs content of jujube powder was 18.55 ± 0.19 mg/g dry weight (DW), which was more than 100 times of those in the unheated jujube powder (0.153 ± 0.003 mg/g DW). Besides, the antioxidant activity of jujube powder after dry-heating process was higher than that of unheated one. As the most abundant AC in the dry-heated jujube powder (12.90 ± 0.75 mg/g DW), N-(1-deoxy-d -fructose-1-yl) proline (Fru-Pro) showed the highest antioxidant activity (62% of equivalent l -ascorbic acid) among 12 ACs in ferric reducing antioxidant power assay. This result provided a method to produce jujube product with high content of ACs and confirmed the positive contribution of Fru-Pro to the antioxidant activity of the jujube powder.     

美拉德反应产物对肠道微生物影响的研究进展

美拉德(Maillard)反应是食品加工、贮藏及烹饪过程中普遍存在的重要反应。Maillard反应会导致蛋白质或氨基酸的胃肠消化性下降,进而增加其进入大肠被肠道微生物发酵利用的可能性。本文主要综述Maillard反应产物对肠道微生物生长及其发酵代谢产物形成等影响的研究进展,旨在为研究Maillard反应产物、肠道微生物与健康的关系提供参考。     

Effects of low concentration of salt and sucrose on the quality of bighead carp (Aristichthys nobilis) fillets stored at 4 °C

The effect of low concentration of salt and sucrose on the quality of bighead carp (Aristichthys nobilis) fillets was evaluated over a 16-day storage at refrigerated temperature (4 °C). Fish samples were brined with 1.1% salt (T1) and 1.1% salt + 0.9% sucrose (T2). The control and the treated fish samples were analysed periodically for physicochemical (pH, total volatile base nitrogen (TVB-N), water loss, electrical conductivity (EC), color), microbial (total viable counts) and sensory characteristics. No significant differences were observed between T1 and T2 for sensory score and EC (p > 0.05). Brining treatments predominantly decreased chemical changes, reflected in TVB-N and pH, retarded water loss and discoloration, inhibited bacterial growth and increased the overall sensory quality of fish, compared to untreated fillets. The results indicated that brining treatments improved the quality and safety of bighead carp fillet, which can be exploited by fish processors.     

Comparison of glucose, glucose 6-phosphate, ribose, and mannose as flavour precursors in pork; the effect of monosaccharide addition on flavour generation

The effect of glucose, glucose 6-phosphate, mannose and ribose on the generation of aroma volatiles in pork was investigated. The monosaccharides were added individually to minced pork prior to heat treatment (160°C for 10min) in the following concentrations: glucose (27.5μmol/g), ribose (1.2μmol/g), mannose (8.3μmol/g) and glucose 6-phosphate (0.5μmol/g). The natural concentrations of the monosaccharides in the pork used were found to be 4.0μmol/g for glucose, 0.1μmol/g for ribose, 0.3μmol/g for mannose and 2.6μmol/g for glucose 6-phosphate. The major aroma compounds identified in the headspace of the heated samples were pyrazines, aldehydes (Strecker and lipid-derived), ketones, and sulphides. Glucose generated the highest amounts of volatiles followed by glucose 6-phosphate. However, when related to the added concentration of glucose 6-phosphate, this phosphorylated monosaccharide showed the highest aroma generating potential. The addition of ribose did not increase the concentration of volatiles compared with pork without the added monosaccharide. The fates of ribose 5-phosphate and ribose in pork were studied over time. The concentrations of ribose and ribose 5-phosphate clearly decreased during 2h equilibration, which may be due to enzymatic activities. These precursors may, therefore, be less important pork flavour precursors than glucose and glucose 6-phosphate.     

Effect of glucose and glycine addition to cocoa mass before roasting on Maillard precursor consumption and pyrazine formation

Cocoa mass was treated with glucose and/or glycine before roasting. For glucose‐treated samples the reductions in reducing sugars and free amino acids were 41.1 and 56.9% respectively, whereas for glycine‐treated samples the respective reductions were 16.2 and 37.4%. The combination of glucose plus glycine treatment led to 39.0 and 48.9% reductions in reducing sugars and free amino acids respectively. For free amino acids the reductions in control and glucose‐treated samples were similar, 56.2 and 56.9% respectively, indicating that the added glucose did not significantly (P < 0.05) influence the free amino acid uptake. When glycine was added, the consumption of free amino acids (37.4%) was lower than for the control and glucose treatments. When glucose and glycine were added, the reduction in free amino acids (48.9%) was lower than for the control and glucose treatments but higher than for the glycine treatment. Apparently, glycine addition inhibited the reducing sugar and free amino acid consumption, whereas glucose addition enhanced the reducing sugar and free amino acid consumption. The glucose plus glycine treatment was similar to the glycine treatment in the contents of 2,5‐dimethyl‐ and trimethylpyrazines. For 2‐methylpyrazine the value for glucose‐treated samples was lower than for control and glycine‐treated samples but almost equal to the value for the glucose plus glycine treatment. It is concluded that the addition of glucose and/or glycine does not affect pyrazine production. © 2002 Society of Chemical Industry     

The retention and recovery of amino acids from pork longissimus muscle following cooking to either 60 °C or 75 °C

Samples of pork longissimus muscle (n = 16) cooked to either 60 °C or 75 °C in a water bath for 90 min were assessed for amino acid composition. Recovery of protein in the cooked meat plus the cooking juice was > 93% and was slightly higher at 60 °C (P = 0.031), but retention in the meat was only 89% and 82% for the lower and higher temperatures (P < 0.0001). Individual amino acids varied in recovery and retention with retention being particularly low for taurine and histidine. The balance of indispensable amino acids was less than ideal, with leucine and valine being the limiting amino acids by about 30% for both raw and cooked pork. Cooking had no detrimental effect on amino acid balance. Some examples of small effects of genotype and sex on amino acid composition of pork were shown.     

Rehydration kinetics at 5 and 15 °C of dry salted meat

The surface of meat products during intermittent drying is successively subjected to dehydration and rehydration processes. The aim of this paper was to study the rehydration kinetics at two temperatures (5 and 15 °C) of salted ground pork, (2% or 4% NaCl) dried to different water contents, (10%, 20% and 35%) using Peleg and Weibull’s models. Surface structure of dried samples was analyzed with electron microscopy and related to rehydration kinetics. The equilibrium water content decreased with temperature and increased with NaCl, but was not affected by the initial water content. The rehydration rate at the beginning decreased with water content and was significantly higher at 5 °C than at 15 °C, but it was not significantly affected by NaCl content. However, the equilibrium water decreased with temperature and tended to increase with NaCl content, but was not affected by the initial water content. High level of dehydration resulted in a more damaged and porous meat matrix. This microstructure may contribute to accelerating the rehydration process.     

Effect of hot-boned pork on the quality of hurdle treated pork sausages during ambient temperature (37 ± 1 °C) storage

The study was aimed at evaluating the suitability of hot-boned pork and pork fat for processing shelf-stable pork sausages using hurdle technology and the different hurdles incorporated were low pH, low water activity, dipping in potassium sorbate solution, vacuum-packaging and post-package reheating. Emulsion stability and cooking yield did not Izatnagardiffer significantly among hot- and cold-processed sausages. Despite the same emulsion pH, the sausages from hot-boned pork had significantly higher fat content. Colour and texture profiles of pork sausages were significantly (P < 0.05) influenced by hot processing. During storage at ambient temperature (37 ± 1 °C), various physico-chemical characteristics, namely pH, TBARS and tyrosine values, of hot- and cold-processed sausages, did not differ. Hot-processing markedly increased the total plate counts of the sausages, but a significant difference was absent for anaerobic counts between treatments at any particular storage interval. Cold-processed sausages had the higher lactobacillus counts throughout the storage period. Sensory evaluation revealed that hurdle-treated pork sausages from hot-boned pork were equally suitable as those from cold-boned pork up to day 6 at ambient temperature.     

Effect of Temperature and Initial Moisture Content on the Chemical Stability and Color Change of Various Forms of Vitamin C

Vitamin C is a widely used food ingredient, and its stability is both important and sensitive to environmental conditions. To monitor chemical and color stability, samples were prepared with varying water contents (0–50 mol water/mol solid) and stored at temperatures (22–60°C) for up to eight weeks. Three common methods (UV/Vis spectroscopy, high performance liquid chromatography, and 2,6-dichloroindophenol titration) were used to monitor chemical stability. Color changes were documented using Hunter colorimeter analysis. Both temperature and moisture content had a significant effect on chemical stability. Browning occurred faster than chemical degradation, and kinetic models were developed for both chemical degradation and color change.     

Effect of thyme essential oil and packaging treatments on fresh Mediterranean swordfish fillets during storage at 4 °C

The present study evaluated the effect of thyme essential oil and packaging on fresh Mediterranean swordfish fillets during storage at 4 °C. Treatments in the present study included the following: air (A), modified atmosphere packaging (M), air with thyme oil (AT) and MAP with thyme oil (MT). Of the physicochemical parameters examined, TBA values for A and M swordfish samples were variable, indicative of no specific oxidative rancidity trend, whereas MT treatment inhibited lipid oxidation in swordfish samples during storage. On the basis of microbiological and sensory data, TMA-N and TVB-N limit values of acceptability for Mediterranean swordfish, of ca. 3.72 and 24.5 mg N/100 g, for the initiation of fresh Mediterranean swordfish spoilage, may be proposed. Of the treatments used in the present study, MT and M were the most effective for the inhibition of pseudomonads and H₂S-producing bacteria in swordfish. Lactic acid bacteria and Enterobacteriaceae (to a lesser extent) were also found to be part of the natural microbial flora of swordfish, irrespective of packaging treatment. Based primarily on sensory data, the shelf-lives of fresh refrigerated Mediterranean swordfish were 8 and 13 days under aerobic and MAP conditions, respectively. Addition of 0.1% thyme essential oil extended the product’s shelf-life under aerobic conditions by 5 days, whereas the combination of MAP and thyme oil resulted in a significant shelf-life extension of the swordfish fillets, i.e. by approximately 7½ days, according to sensory data, as compared to the control sample.     

Green tea – A potential preservative for extending the shelf life of fresh mutton at ambient temperature (25 ± 2 °C)

This investigation was taken up to evaluate the feasibility of using green tea (GT) to extend the shelf life of fresh mutton, at ambient storage conditions (25 ± 2 °C and 85 ± 5% RH). The ethanolic extract of GT (GTE) was found to significantly inhibit (P < 0.01) spoilage microflora, including certain pathogens of acidulant treated mutton (pH 3.8) for up to 4 days. Application of GTE did not cause any deleterious change in sensorial and physical quality and the mutton was acceptable for up to 4 days. While the control samples showed initial signs of spoilage between 20 and 24 h and registered an increase in free fatty acids (FFA) from 1.24 g to 4.1 g/100 g lipid and biogenic amine index (BAI) from 0.27 mg to 4.63 mg/100 g mutton, at the end of two days of storage, the GTE treated sample showed FFA levels of 1.5 g/100 g lipid and BAI of 0.25 mg/100 g mutton at the end of the 4 days. GTE treatment could be effectively used to extend the shelf life of fresh mutton for up to 4 days in Indian climatic conditions, since it significantly (P < 0.01) inhibits the formation of these lipolytic and proteolytic degradation products, which are responsible for sensorial spoilage.     

Effect of micronisation temperature (130 and 170 °C) on functional properties of cowpea flour

Functional properties of cowpea flour from seeds micronised at two different surface temperatures (130 and 170 °C) were studied. Micronisation (130 and 170 °C) significantly (P ? 0.05) increased the water absorption capacity and least gelation concentration of the flour. The treatment significantly (P ? 0.05) reduced the water solubility and swelling indices, gel strength and foaming capacity of the flour. The changes in cowpea flour functional properties, such as the loss of foaming capacity in flours from micronised (130 and 170 °C) seeds, were associated with significant (P ? 0.05) increase in the surface hydrophobicity and cross-linking of the cowpea protein. SDS–PAGE of the protein-rich fractions revealed changes in the protein subunit profile which included the formation of disulphide bonds and possibly Maillard cross-links. The flour from M-170 °C seeds was significantly (P ? 0.05) darker than was the flour from unmicronised and M-130 °C seeds.     

The influence of the pH value on the formation of Strecker aldehydes in low moisture model systems and in plant powders

 Strecker aldehydes are regularly found in the low boiling point fraction of volatile compounds of processed plant foods. They are produced via the Strecker degradation of amino acids. The formation of 3-methylbutanal (3-MB) in a glucose- and leucine-containing low moisture model system and the formation of acetaldehyde, 2-methylpropanal, 2-methylbutanal and 3-MB in plant powders showed a linear pH dependence. The formation of the Amadori rearrangement product (ARP) fructose-leucine (fru-leu) in the model system, in contrast to it's degradation, was not influenced by the pH. The formation of the 3-deoxyosone [3-deoxy-d-erythro-hexos-2-ulose (3-DH)] by degradation of fru-leu was slower at pH 7 than at pH 5 suggesting that it is either less stable at pH 7 or being formed to a lesser extent. Further experimental results suggested that enolisation and retro aldol reactions of reducing sugars also contribute to the production of Strecker aldehydes as the pH is increased, by creating α-dicarbonyl compounds. The appearance of fructose in the glucose-containing model systems indicates enolisation reactions in the course of a Maillard reaction. Received: 2 November 1999     

Chemical and biochemical changes of hybrid catfish fillet stored at 4 °C and its gel properties

Chemical and biochemical changes of aquacultured hybrid catfish fillet (Clarias macrocephalus × Clarias gariepinus) and its gel-forming ability as affected by age and sex of fish along with storage time were investigated. Fillets were stored at 4 °C for 0, 3, 6, 9, 12 and 15 days. There was no significant effect of sex and age of fish as well as storage time on fat, moisture and ash contents (P > 0.05). The total protein, water soluble protein, and salt soluble protein contents of the fillets significantly decreased with storage time (P < 0.05). On the other hand, pH, total volatile base nitrogen (TVB-N) and autolytic degradation products (ADP) increased as storage time continued (P < 0.05). Decreases in Ca²⁺-ATPase activity and gel properties were observed as storage time increased. However, there was no significant effect of either sex or age of fish on textural properties of gel (P > 0.05). Hybrid catfish fillet stored at 4 °C should be processed within 6 days.     

反应温度和时间对抗坏血酸/精氨酸Maillard反应体系中挥发性化合物形成的影响

采用顶空固相微萃取-气相色谱-质谱联用技术对抗坏血酸/精氨酸反应体系在不同反应温度和时间下的产物进行鉴定,共鉴定出包括吡嗪、醛、呋喃、醇和吲哚在内的24种化合物,其中14种吡嗪化合物为主要香味化合物。考察了反应温度和时间对产物特别是对吡嗪化合物的影响。结果表明,随着反应温度的升高和反应时间的延长,吡嗪类化合物的总量均增加;其中,随反应温度的升高,相对其他吡嗪化合物2-乙基-6-甲基吡嗪、3-乙基-2,5-二甲基吡嗪的量明显增加;随反应时间的延长,2-乙基-6-甲基吡嗪的量明显增加。