Reactivity of sorbate and glycerol in intermediate moisture meat products

Intermediate moisture meats were prepared by cook-soak equilibration with glycerol/salt, sucrose/salt or salt only solutions to an a_w of 0.85. Sorbate or propionate was added to some products and all were stored at 38°C in the presence of air. It was found that sorbate, but not propionate, caused increased rates of protein aggregation and accelerated loss of haemoprotein character. Glycerol may also take part, albeit more slowly, in these deteriorative reactions. However, sorbate did not appear to lead to any marked increase in the rate or extent of the reactions leading to solubilisation of the collagen present in these samples; glycerol, however, significantly increased the rate and extent of such reactions. The results are discussed in the light of the results obtained with the model systems described in the previous paper.     

Reactivity of glycerol in intermediate moisture meats

Non-enzymic browning (NEB) reactions between glycerol and some of the amino acids present in meat have been observed at 38 and 65°C; l-lysine is the most reactive of the amino acids studied and l-cysteine and l-arginine the least. These NEB reactions also occur between glycerol and proteins (gelatin and casein). The reactions are not unique to glycerol as other polyhydric alcohols also form brown pigments with lysine. On prolonged air storage at 65°C glycerol itself undergoes mild oxidation, ultimately yielding a brown solution.     

Characteristics of some intermediate moisture smoked meats

Intermediate moisture smoked beef was prepared by cook-soak/equilibration in a solution containing sodium chloride, sodium nitrite and potassium sorbate. Two further solutions contained glycerol and glycerol + 'onion' in addition to the above ingredients. Half the samples in each treatment group were smoked for 18 h (heavy smoking) and the others for 4 h (light smoking) at 50°C. All samples developed the pink-red colour of nitrite cured meat but those treated with glycerol were darker, presumably due to decreased moisture contents. Glycerol increased the apparent moisture, fat and sodium dodecyl sulphate (SDS) soluble protein contents and also improved the conversion of haemoproteins to the cooked cured form but decreased the percent soluble hydroxyproline. Smoking caused a marked decrease in moisture, SDS-soluble protein and soluble hydroxyproline contents and slightly decreased the available lysine and percent conversion of the haemoproteins to the cured nitrose forms. Smoking also caused increased darkening and hardness of the samples. Total viable aerobes, coliforms and fungi were below the levels of detection while TBA values were low and all samples possessed no detectable rancidity. Electrophoretograms of the samples indicated that cooking/equilibration had no significant effects on the proteins present but smoking led to a slight loss of some of the protein components.     

The role of lipids and glycerol in determining the shelf-life of glycerol desorbed intermediate moisture meat products

During storage of glycerol desorbed intermediate moisture beef at 38°C the marked loss of eating quality, demonstrated by increasing loss of nitrogen solubility in sodium dodecyl sulphate (SDS) plus β-mercaptoethanol, loss of haemoprotein character, decrease in pH and the formation of water-soluble hydroxyproline containing fragments, is not markedly affected by the presence of oleic acid and/or butylated hydroxytoluene. In addition, gas-liquid chromatographic analysis of the lipid fractions suggests that, in these meats, the relative composition of the neutral phospholipid fractions does not change to any marked extent during storage. However, the TBA and peroxide values, which are very high in the freshly prepared meats, do decrease quite markedly during storage. Consideration of these results suggests that, in glycerol desorbed meats, glycerol oxidation products are the major reactants leading to loss of eating quality.     

Stability of sorbic acid in intermediate moisture systems

Intermediate foods are a heterogeneous group of foods which are stabilized by lowering their water activity to a level insufficient to support bacterial growth, typically about 0.85. However, moulds and yeasts are able to grow at these water activities and it is usual to add an antimycotic such as sorbate to ensure microbial stability. Sorbate, though, is liable to oxidation and in model systems adjusted to a water activity of 0.85 some of the oxidation products were found to be potential reactants in non-enzymic browning reactions with lysine, glutamate and haemoglobin solutions when stored at 38 degrees C or 65 degrees C. Oxidation led to an increase in pH and the formation of thiobarbituric acid-reactive substances. In some intermediate moisture meat products prepared by cook-soak equilibration in a variety of humectant solutions, 0.3% sorbate induced the formation of covalent linkages between proteins on storage at 38 degrees C. The concentration of sorbate in the meats decreased by a factor of 2 during 4 months at this temperature. The effects of such reactions on the quality of the food are discussed.     

Evaluation of the efficacy of four weak acids as antifungal preservatives in low-acid intermediate moisture model food systems

The potential efficacy of four weak acids as preservatives in low-acid intermediate moisture foods was assessed using a glycerol based agar medium. The minimum inhibitory concentrations (MIC, % wt./wt.) of each acid was determined at two pH values (pH 5.0, pH 6.0) and two a_w values (0.85, 0.90) for five food spoilage fungi, Eurotium herbariorum, Eurotium rubrum, Aspergillus niger, Aspergillus flavus and Penicillium roqueforti. Sorbic acid, a preservative commonly used to control fungal growth in low-acid intermediate moisture foods, was included as a reference. The MIC values of the four acids were lower at pH 5.0 than pH 6.0 at equivalent a_w values, and lower at 0.85 a_w than 0.90 a_w at equivalent pH values. By comparison with the MIC values of sorbic acid, those of caprylic acid and dehydroacetic acid were generally lower, whereas those for caproic acid were generally higher. No general observation could be made in the case of capric acid. The antifungal activities of all five weak acids appeared related not only to the undissociated form, but also the dissociated form, of each acid.     

Reactivity of acrylamide with coffee melanoidins in model systems

Coffee and its substitutes have been described as complex matrices for acrylamide (ACR) analysis due to both analytical interferences and ACR instability in the matrix. Melanoidins are multifunctional and biochemically active polymers which are formed in large extent during coffee roasting. Model systems composed of ACR (elimination studies) or glucose-asparagine (ACR formation/elimination studies) with/without melanoidins was heated at 180 °C. Washed sea sand and cellulose microcrystalline were used as matrix. Coffee melanoidins had a direct influence on the fate of ACR under heating, while the effect was not observed at room temperature. In addition, ACR decrease was also related to the reaction time and the initial amount of melanoidins in the media, where clearly a dose-response was observed. In contrast, pH (from 3.5 to 7.0) had no significant effect on ACR reactivity towards melanoidins. It is hypothesized that nucleophilic amino groups of amino acids from the proteinaceous backbone of melanoidins react via the Michael addition reaction with ACR, although the exact mechanism is unknown. Then, melanoidins could modulate the reaction pathways of ACR formation and elimination during coffee roasting and serve as acrylamide-mitigation substance.     

甘油施加比例对加热卷烟水分、烟碱和甘油分布的影响

目的：优化加热卷烟烟草薄片的工艺参数。方法：制备了甘油添加比例为5%~30%的12个梯度等级的加热卷烟烟草薄片,制成加热卷烟烟支。使用GC-TCD方法检测加热卷烟烟气、滤嘴冷凝段和烟芯段中水分、烟碱和甘油质量,分析主要成分的质量分布特点,以及释放率、截留率和转移率。结果：加热卷烟烟草薄片在5%~30%甘油添加比例下,水分释放率较高为88.6%~92.3%,主要分布在烟气和滤嘴冷凝段;烟碱释放率次之,为25.5%~34.2%,主要分布在滤嘴冷凝段和烟芯段;甘油释放率最低,为13.9%~21.3%,主要分布在烟芯段。结论：当烟草薄片选择10%~18%的甘油添加比例时,加热卷烟的烟碱和甘油具有较高的转移率和较低的截留率。     

Study of benzoate, propionate, and sorbate salts as mould spoilage inhibitors on intermediate moisture bakery products of low pH (4.5-5.5)

A hurdle technology approach has been applied to control common mold species causing spoilage of intermediate moisture bakery products (Eurotium spp., Aspergillus spp., and Penicillium corylophilum), growing on a fermented bakery product analogue (FBPA). The factors studied included a combination of different levels of weak acid preservatives (potassium sorbate, calcium propionate, and sodium benzoate; 0-0.3%), pH (4.5-5.5), and water activity (a(w); 0.80-0.90). Potassium sorbate was found to be the most effective in preventing fungal spoilage of this kind of products at the maximum concentration tested (0.3%) regardless of a(w). The same concentration of calcium propionate and sodium benzoate was effective only at low a(w) levels. On the other hand, potassium sorbate activity was slightly reduced at pH 5.5, the 0.3% being only effective at 0.80 a(w). These findings indicate that potassium sorbate may be a suitable preserving agent to inhibit deterioration of a FBPA of slightly acidic pH (near 4.5) by xerophilic fungi. Further studies have to be done in order to adjust the minimal inhibitory concentration necessary to obtain a product with the required shelf life.     

Sorbic acid diffusivity in relation to the composition of high and intermediate moisture model gels and foods

The diffusivity at infinite diffusant dilution ( D ₀) of sorbic acid in high and intermediate moisture gels (with various substrates and water contents) and in three foods was evaluated. The determination of D ₀(25°C) was achieved by tridimensional diffusion in gels cubes or by monodimensional diffusion in infinite food columns. For the same substrate concentration by weight, D₀ values of sorbic acid in concentrated sugar solutions decreased slightly when the molecular weight of the sugar was increased. When a liquid substrate such as glycerol was used, D ₀ values referred to equal concentrations by weight, were higher than in sugar solutions. The diffusion of sorbic acid is related, as a first approximation, to the water content rather than to the water activity of the diffusion medium.     

Effect of sweet solutes and potassium sorbate on the thermal inactivation of Z. bailii in model aqueous systems

The effect of solute type (glucose and polyols) and potassium sorbate (KS) on Zygosaccharomyces bailii thermal inactivation was evaluated in acidified aqueous model systems. Thermal inactivation curves obtained were fitted with Baranyi equation and parameters of this model were estimated and used to establish the effect of water activity (a_w), solute added and KS on Z. Bailii survival. Results obtained showed that addition of KS (0.025%, w/w) in general promoted an increase in the rate of heat inactivation. The use of polyols to depress a_w to 0.985 in the absence of KS produced no effect on rate of heat inactivation. On the contrary, the use of glucose (10%, w/w) enhanced it. This trend was also observed when a_w was depressed to 0.971 by glucose or xylitol or glucose-polyols. Moreover, a_w depression in systems containing KS produced different effects on thermal inactivation rate depending on system composition. A synergic effect on the rate of inactivation of Z. bailii was observed by the combined use of KS and sorbitol, xylitol or glucose to depress a_W to 0.985–0.988. This behavior might allow to decrease the severity of the thermal treatment with no detrimental effect on sterility.     

Inclusion of the variability of model parameters on shelf-life estimations for low and intermediate moisture vegetables

Shelf-life is the time period during which products retain market-acceptable quality while meeting legal and safety requirements. Deterministic models yield single value estimations of shelf-life typically based on average or worst-case values for input parameters. In deterministic calculations, considering the input parameter variability can be challenging. In this study, a Monte Carlo procedure and the G.A.B. model for moisture sorption isotherms were used to predict shelf-life frequency distributions for intermediate moisture (IM) tomato slices, and low moisture (LM) onion flakes and sliced green beans. End of shelf-life for IM tomato slices (initial a_w = 0.8) was assumed to occur for a 10% moisture loss, and when a_w changed from 0.25 to 0.4 for LM onion flakes and LM sliced green beans. The estimated shelf-life for tomato slices, LM onion flakes, and LM sliced green beans based on the deterministic approach was 243, 86, and 79 days, respectively. The Monte Carlo procedures yielded shelf-life frequency distributions with values ranging 181–366, 76–95, and 71–90 days, respectively. Products would fail before the deterministic shelf-life value with an unacceptably high probability of 51.6, 48.6, and 53.0%, respectively. If 5% is an acceptable probability that the actual shelf-life is shorter than specified, the estimated values would be 211, 81, and 73 days, respectively. X_m and K were the most influential G.A.B parameters on the shelf-life of the three products. The package area, product amount, and water vapor transmission rate were high contributors and had the expected effect on shelf-life as demonstrated by deterministic estimations.     

Application of Ross' equation for prediction of water activity in intermediate moisture food systems containing a non-solute solid

This work investigates the use of the Ross (1975) equation for the prediction of water activity (a), in aqueous electrolyte or non-electrolyte solutions to which a non-solute (casein) was added. Water activity of the ternary mixtures (casein-water-solute) was in the range of a, = 0.85-0.90 which is of interest for the development of intermediate moisture foods for human consumption. It was found that the use of the Ross equation coupled with a correction for the water strongly bound to casein gives good predictions of a.     

叶丝气流干燥过程中水分和丙三醇迁移特性

为了在叶丝气流干燥过程中有效调控物料的水分和丙三醇含量,考察丙三醇含量和干燥温度对叶丝中丙三醇和水分迁移的影响,利用固定床气流干燥装置,在100～145℃下对丙三醇含量为0～6.6%的叶丝进行干燥试验,得到了叶丝中丙三醇和水分释放规律。结果表明：(1)添加丙三醇后叶丝水分迁移规律基本一致,叶丝的干燥速率受丙三醇初始含量的影响较小。干燥过程分为两个阶段,第一阶段（0～100 s）和第二阶段（100～600 s）。(2)叶丝表面温度与干燥温度正相关,与丙三醇的初始含量无关。(3)丙三醇初始含量对其脱除无显著影响。第一阶段丙三醇的损失量基本相同,约占总损失量的50%以上;第二阶段不同丙三醇初始含量的损失速率无明显差异,且随着干燥时间的增加不断减小。(4)干燥温度对丙三醇脱除有显著影响。第一阶段不同干燥温度下丙三醇损失量均为0.6百分点左右,损失速率随干燥时间线性降低,损失速率的变化率与干燥温度呈负相关关系;第二阶段丙三醇损失量随干燥温度的升高而增大,损失速率基本保持稳定。     

Use of potassium sorbate, diethylpyrocarbonate and heat for the preservation of prunes at high moisture levels

Normal mould and yeast growth causing spoilage in prunes containing 69% moisture could be prevented by heat processing. At 57% moisture, a dip in 10% potassium sorbate solution was effective for 40–50 days. At 43% moisture, a 5% potassium sorbate dip provided protection and at 34% even a 2% potassium sorbate dip or 550 ppm diethylpyrocarbonate was adequate to inhibit the mould and yeast growth during the 90 day duration of this study.     

Measurement of non-enzymic browning of dehydrated and intermediate moisture meat

Non-enzymic browning (NEB) of a traditional intermediate moisture meat (den-deng) and dehydrated meat was measured by both aqueous trypsin digestion and lead acetate-ethanol precipitation methods. Trypsin digestion did not interfere with NEB determination, and the addition of a glucose-glycine NEB mixture to dendeng had no effect on NEB measured by the lead acetate-ethanol precipitation method. Comparison of NEB measurements by the lead acetate-ethanol precipitation method and an aqueous trypsin digestion method on dendeng containing added myoglobin and/or haem pigments showed that only the lead acetate-ethanol precipitation method overcame errors which were due to the presence of these pigments. Spice pigments present in dendeng also interfered and led to high NEB values, while NEB increased markedly in the presence of coconut sugar. Results for NEB of dendeng and dehydrated meat stored for up to 12 weeks at 50°C were lower when measured by the lead acetate-ethanol precipitation method compared to results by the aqueous trypsin digestion method, although both methods showed that NEB increased with storage time.     

Interactions between aspartame, glucose and xylitol in aqueous systems containing potassium sorbate

The interaction between aspartame, glucose and xylitol in aqueous model systems of pH 3.00 and containing potassium sorbate was studied. Potassium sorbate degradation diminished with the increment of aspartame level from 0.050 to 0.500 g/100 g of system. Xylitol was the humectant that minimized aspartame degradation and non-enzymatic browning development. In general, as expected, presence of aspartame, xylitol or glucose and their mixtures increased the sweetness and they also diminished the sourness of the systems. The addition of 0.050 g of aspartame/100 g of system to the system containing xylitol produced a synergistic effect on sweetness intensity. Based on that trend, it could be concluded that the use of more than one sweetener might allow diminishing the amount of each one of them to assure a specific sweet level.These results stand out the advantage of the use of xylitol as well as the importance of an appropriate choice of the additives and food ingredients to use in the formulation of modified products with lower sugar content to optimize their quality.