Changes in physicochemical characteristics of rice during storage at different temperatures

This study investigated the changes in the physicochemical properties of rice during storage at different temperatures. Milled rice stored at high temperatures showed higher fat acidity than rice stored at low temperatures. Although the moisture content of milled rice stored at 30 °C and 40 °C decreased below 15.5% (15.33% and 15.22%, respectively) after 1 month, adequate values were maintained with storage at 4 °C for 3 months (15.50%) and at 20 °C for 2 months (15.53%). Rice stored at low temperatures retained its white coloration, whereas low color retention values were obtained at higher storage temperatures. Peak viscosity increased during 4 months of storage and larger changes were found at higher storage temperatures. Breakdown decreased and setback increased with storage, regardless of storage temperatures. Storage at higher temperatures increased cohesiveness and hardness in compared with storage at lower temperatures. High temperatures also led to a decrease in adhesiveness with age. High temperatures (30 °C and 40 °C) significantly decreased all sensory values even after 1 month of storage. These results are similar to those obtained in an analysis of cooked rice texture. The results of this study indicate that storage temperature is an important factor affecting the physicochemical properties of rice. Short storage periods below room temperatures are recommended to maintain rice quality.     

Physicochemical and pasting properties of maize as affected by storage temperature

Maize grains are used as raw material in various food products. In countries where the production is seasonal, the grains must be stored throughout the year in order to provide sufficient maize supply for the food industries and consumers. During storage, the environmental temperature is considered as one of the most critical variables that affects grain quality. This study aimed to evaluate the effects of various storage temperatures (5, 15, 25 and 35 °C) on the proximate composition, pH, fat acidity, percentage of grains infected by molds, grain color, protein solubility and pasting properties of maize stored for 12 months. Grains stored at 35 °C during the 12 months period showed the greatest decrease in grain yellowness, pH, protein solubility and breakdown viscosity. An increase in disulfide bonds within the protein structure and interaction between starch and non-starch components seems to be responsible for the changes in protein solubility and pasting properties determined in maize during the storage period. Fat acidity and the percentage of grains infected by visible molds were concluded to be very dependent of moisture content. The result of this study demonstrated that the minimum temperature of 5 °C was able to maintain the quality of maize stored for up 12 months.     

Study on retrogradation of maize starch–flaxseed gum mixture under various storage temperatures

This study aimed to investigate the effect of flaxseed gum (FG) on the retrogradation of maize starch (MS) gels under different storage temperatures. In this work, MS‐FG gels with 0–0.4% FG were stored under different temperatures (–20, 4 and 20 °C). Under all storage temperatures, the addition of FG inhibited the retrogradation process of MS, suppressed the recrystallisation of starch molecules, reduced the water loss of starch gels and improved the texture of the gels. Among the three storage temperatures, ?20 °C could almost stop the starch retrogradation but leading it results in the hardest gel texture. The retrogradation of MS‐FG gels stored under 4 °C was most serious with the fastest rate of recrystallisation. When stored at 20 °C, the gels had a retrogradation degree that was lower than when they were stored at 4 °C and also had the softest texture.     

Nutritional changes in maize (Zea mays) during storage at three temperatures

Nutritional changes in maize grains stored at 10, 25 and 45 °C for 6 months were studied. Significant decrease in pH and increase in titratable acidity was observed during storage of maize grains at 25 and 45 °C. Moisture contents of maize grains decreased by 25% at 25 °C and 38% at 45 °C after six months of storage. Total soluble sugars increased by 10.7% at 10 °C and 17.3% at 25 °C, whereas a 39.5% decrease was observed after 6 months storage at 45 °C. Total available lysine and thiamine contents in maize grains decreased by 13 and 9.26% at 25 °C, 16 and 20.4% at 45 °C, respectively, after 6 months of storage. Protein digestibility decreased by 5.19 and 9.0% at 25 and 45 °C, respectively, whereas decrease in starch digestibility was 9.86% at 25 °C and 15.1% at 45 °C on storage of maize grains for 6 months. However, no significant nutritional changes occurred during storage of maize grains at 10 °C.     

Some Characteristics of Whole Corn: Whole Soybean (70:30) and Rice: Whole Soybean (70:30) Mixtures Processed by Simple Extrusion Cooking

Mixtures of corn or rice with dehulled soybeans (70:30) were extruded at three cone openings. Processing temperatures were inversely correlated with cone opening. As cone opening increased fat retention and nitrogen solubility index increased, while dispersibility, protein nutritive value and acceptability (as “atole”) by school children decreased. The PER and NPR of the mixtures were significantly (P < 0.05) correlated with processing temperature (r = 0.90 for both) and sensory score (r = 0.83 and 0.82, respectively). No correlation was observed between protein nutritive value and residual antiphysiological factors of the products. After storage of mixtures for 12 wk at 4° and 25° C, fat acidity values were lower than 2%; those stored at 35°C showed nearly 10%. All samples were equally acceptable.     

Influence of CMC‐ and guar gum‐based silver nanoparticle coatings combined with low temperature on major aroma volatile components and the sensory quality of kinnow (Citrus reticulata)

Aroma profile and organoleptic quality of CMC‐ and guar gum‐based silver nanoparticle‐coated kinnow (Citrus reticulata cv. Blanco) was evaluated for 120 days at 4 °C and 10 °C, 85–95% relative humidity. Loss in three major aroma‐active volatile compounds (limonene, linalool and γ‐terpinene) was determined after every 15 days by GC‐MS. Sensory quality of coated and uncoated fruit stored at 10 °C was declined during storage. Twenty five volatile aroma compounds were identified in fresh kinnow juice. Guar gum‐Ag coatings and 4 °C storage has significantly reduced losses of limonene, linalool and γ‐terpinene contents from 91 to 23%, 99 to 10% and 97 to 29% respectively as compared to uncoated fruit stored at 10 °C. Study suggests that CMC‐ and guar gum‐based silver nanoparticle‐coated kinnow stored at 4 °C has preserved the fruit aroma and sensory quality for 120 days.     

Sensory changes in extruded oat stored under different packaging,light and temperature conditions

The sensory quality of extruded oat, stored in light and darkness in packages with different oxygen transmission rates (including the use of an oxygen absorber), was evaluated after 3 months of storage at 38 °C and 10 months of storage at 23 °C. To reduce the costly and time consuming shelf life and packaging evaluation, the possibility of reducing the number of sensory attributes to be analyzed and to accelerate shelf life testing was studied.The intensity of oat odor, paint odor and crispiness were found to describe the main differences among the samples. By increasing the temperature from 23 to 38 °C for samples stored in darkness, packaging evaluation tests for extruded oat might be performed in approximately one third of the time. Changes in headspace oxygen concentration in the packages due to oxygen consumption were in agreement with the sensory changes in the oat.     

Storage of hybrid rough rice – Consideration of microbial growth kinetics and prediction models

The objective of this study was to determine kinetics of mold growth on popularly grown hybrid long-grain rough rice during storage at conditions that simulate delayed drying and prolonged storage. Three long-grain hybrid rice cultivars, XL753 (2014) and CL XL745 (2014, 2015) and XL760 (2015) conditioned to four different moisture contents (MCs) (12.5%, 16.0%, 19.0%, and 21.0% wet basis) were stored in rough rice form at temperatures ranging from 10 °C to 40 °C for a period of 16 weeks. The study was repeated using rice from two consecutive crop seasons, 2014 and 2015. For all cultivars, a direct relationship between mold counts and rice MC was observed – whereas more complex trends were observed for the effect of temperature and the duration of storage on mold growth. Kinetic models including Baranyi, Weibull, Gompertz, Richard and Buchanan were successfully modified and fitted using non-linear regression and used to predict the mold counts (log₁₀ CFU/g) for varying conditions (correlations = 0.65–0.76). The study concluded that long-grain hybrid rough rice could be stored at low MC levels (≤17%) and moderate temperatures (≤27 °C) for up to 6 weeks without any change in the mold growth profile. However, storing rice at high MC (>17%) for more than 8 weeks, especially at higher (>27 °C) temperatures should be avoided due to the potential for high mold activity leading to loss of the grain quality.     

Selected Quality Attributes of Fine Basmati Rice: Effect of Storage History and Varieties

Storage period, temperature and moisture are the key traits, accountable for variation in chemical, cooking and sensory attributes of rice. The study of two promising varieties of fine Basmati rice stored at various temperatures revealed pronounced influence of storage on various quality traits i.e. volume expansion ratio, water absorption ratio, elongation ratio, alkali spreading value, amylose contents and sensory attributes. The cooking quality was affected significantly in the months following harvesting. Freshly harvested Basmati varieties (Basmati Super and Basmati-385) were aged for a period of sixteen weeks (4 months) at different temperatures (5, 25, 35, and 45°C). Aging of rice played imperative role in establishing the aforesaid quality traits. Storage condition resulted in increased moisture, water absorption ratio, volume expansion ratio and elongation ratio while amylose content and alkali spreading value of both rice varieties were decreased. The protein content showed insignificant differences. Storage of both varieties at 35°C gave best results for sensory attributes like taste and over all acceptability. Basmati Super showed better performance in cooking and eating quality than that of Basmati-385 during storage.     

Effect of storage temperature on rice thermal properties

Study on the gelatinization kinetics of rice showed that gelatinization process was divided into two steps: swelling of the amorphous region and disruption of the crystalline region. Higher temperature storage (37 °C) resulted in an increase in the breaking point temperature suggesting that energy for the disorder of these two regions of starch in rice stored at 37 °C was higher than the rice stored at 4 °C. Storage-induced changes in rice led to significant increases in DSC peak temperature (p < 0.05) and significantly broadened peak width (p < 0.01) for rice stored at 37 °C compared to rice stored at 4 °C. As the peak temperature of rice stored at 37 °C was not influenced by the “annealing” treatment in contrast with the increased peak temperature of rice stored at 4 °C after the “annealing” treatment, the results indicate that the ageing process (37 °C storage) has already re-ordered the rice grain structure and that the annealing process under these conditions has no further effect on starch thermal properties. Because starches isolated from rice grain stored at 4 °C and 37 °C had similar thermal properties, this implies that the effects of storage on thermal properties are associated with the interactions between starch and non-starch components following storage. The gelatinization endotherm shifted to a lower temperature (p < 0.01) and a narrowed peak width was achieved after cellulase and protease treatments of stored rice, which indicates that the changes in cell wall remnants and proteins are responsible for the changes in rice thermal properties during storage. Scanning electron microscopy was applied to visualize the treatments of cellulase and protease on rice.     

Ensuring the best storage temperature of Egyptian pastrami based on microbiological,physico-chemical and sensory evaluation

Egyptian pastrami is among the most important and widely consumed meat products in Egypt and due to the great defects in its storage as a ready-to-eat products by retailers, distributers or even consumers, the aim of the current research is to assess the effect of storage temperatures on physico-chemical, microbiological, and sensory properties of Egyptian pastrami using autoclaved non-meat ingredients to ensure the best storage temperature of such important food. Four storage temperatures were applied including room temperature during summer (25 °C), room temperature during winter (15 °C), in fridge at 4 °C and in freezer at −18 °C for a period of 60 days using whole unsliced produced pastrami arms. The findings showed that there was no significant effect (P > 0.05) of storage temperatures on the physico-chemical and sensory properties of tested Egyptian pastrami as the four types were highly accepted based on the physico-chemical and sensory evaluation. Meanwhile, there was noticeable effect of storage temperatures on the microbiological properties of the four manufactured types of pastrami, as the samples stored at −18 °C or at 4 °C for 60 days had the lowest microbial loads and was the best from microbiological aspect.     

Impacts of Low and Ultra-Low Temperature Freezing on Retrogradation Properties of Rice Amylopectin During Storage

Amylopectin retrogradation is a serious problem in starch-based ready meals. In the current research, rice amylopectin was frozen by low temperature (−20, −30, and −60°C) and ultra-low temperature (−100°C), and then stored at 4°C for 21 days or at −18°C for up to 5 months to evaluate the retrogradation properties. Amylopectin retrogradation enthalpy of rice was determined by a differential scanning calorimetry. The results showed that low temperature and ultra-low temperature freezing can effectively retard amylopectin retrogradation during the freezing process and during frozen storage (−18°C) for at least 5 months. However, rice amylopectin still retrograded after the freezing process during chill storage at 4°C. The methods of low and ultra-low temperature freezing combined with frozen storage might be potentially very useful for food industry to produce high quality starch-based ready to eat meals.     

Effect of ageing-induced changes in rice physicochemical properties on digestion behaviour following storage

The changes in rice grains structure and digestion behaviours were investigated following storage at 4 °C and 37 °C, respectively. Pasting study indicated that rice samples stored at 37 °C demonstrated a consistent increase in the time to peak viscosity of the Rapid ViscoAnalysis parameters, implying a quick ageing progress. Compared to the rice stored at 4 °C, aged rice (stored at 37 °C) showed a coarser morphology after cooking by SEM, suggesting a limited starch gelatinization. Consistently, ageing process led to a decrease in the leaching of starch molecules in cooking residual water, which further confirmed that starch granules in aged rice grain caused less hydration and swelling. The analysis of the amount of cell wall remnants showed that rice stored at 37 °C caused a significant increase in the amount of cell wall remnants along the storage at 37 °C, which might suggest that the cell wall structure of the rice grains became more lignified because of the ageing. Furthermore, the ageing process significantly reduced rice digestion kinetics both in rate and extent. Thus, it is assumed that ageing process leads to the cell walls becoming more strengthened and lignified, which makes the rice grain more organized in its structure, and subsequently reduces starch granules disruption and molecules leaching during the cooking. Therefore, this study suggests that the changes in digestion behaviours of rice are highly associated with the changes in rice physical and chemical properties occurred during storage and the ageing process might be another option for manipulating rice digestion properties.     

Microbiological and Sensory Changes in Minced Beef Treated with Potassium Lactate and Sodium Diacetate during Refrigerated Storage

The effect of potassium lactate and sodium diacetate on the microbiological changes and sensory properties of vacuum-packaged minced beef was investigated. The meat samples both with a preservative (in the amounts 0.65% and 1.3%) and without were stored at temperatures of 0–1°C and 5–6°C. The influence of storage time on changes in total bacteria count (TBC), lactic acid bacteria (LAB), Brochothrix thermosphacta, and the microbes of the Enterobacteriaceae family was investigated, as well as changes in pH and sensory quality. It was found that the addition of the preservative to the minced meat caused a significant extension (p < 0.05) of the lag phase and an inhibition of microbial growth rate, depending on temperature, storage time, and its concentration. The antibacterial effect was significantly higher (p < 0.05) at a temperature of 0–1°C than at 5–6°C and most susceptible to it were the bacteria belonging to the Enterobacteriaceae. The study results showed that the minced beef containing the preservative which had been vacuum stored at 0–1°C, presented a better sensory quality and had a shelf-life of about 6 days longer, in relation to the quality and shelf-life of the control samples. For each of the refrigeration storage temperatures however, there was no statistically significant change (p < 0.05) in the pH for the various storage periods and preservative quantities present.     

Fourier transform infrared spectroscopy analysis of physicochemical changes in UHT milk during accelerated storage

The feasibility of using Fourier transform infrared spectroscopy (FTIR) to detect heat induced conformational rearrangements of proteins, protein–protein and protein–lipid interactions was studied with accelerated shelf-life protocols. Ultra-high temperature treated whole (WM) and skim milk (SM) were stored at 20, 30, 40 and 50 °C for 28 days. The changes leading to increased sedimentation in SM and WM at higher temperatures (≥40 °C) were observed during first 14 days of the storage period. Milk samples stored at 40 and 50 °C showed marked changes in the bands corresponding to conformations of milk lipids and formation of intermolecular β sheet of proteins, indicating protein–lipid interactions and aggregation. Dried sediment contained fat confirming protein–lipid participation in the sedimentation. FTIR was also able to detect changes that led to increased sedimentation in SM at temperatures lower than 40 °C, but only after 28 days.     

Accelerated aging of jasmine brown rice by high-temperature fluidization technique

After being cooked, newly harvested brown rice becomes a pasty mass and swells only slightly. To modify these undesirable brown rice properties, the paddy needs to be stored for at least 3–6 months. However, problems arise since brown rice has short shelf-life (3–6 months) due to accumulation of free fatty acids (FFA) leading to rancidity during storage. In the present study, high-temperature fluidized-bed drying technique in combination with tempering step was tested to alleviate the above-mentioned problems. The quality of rice dried at temperatures of 130 and 150 °C and tempered for 30 up to 120 min was compared to that of brown rice stored at ambient temperature (approximately 30 °C) for 7 months. The experimental results showed that the cooking and eating properties of the fluidized bed dried brown rice, i.e., hardness, solid loss, volume expansion and elongation ratio, changed in a similar fashion to those of the conventionally aged brown rice. The drying temperature and tempering time affected significantly the brown rice properties. The texture of cooked thermally treated brown rice was significantly firmer than that of the conventionally aged brown rice. In addition, it was found for the thermally treated brown rice that the contents of free fatty acids increased only slightly during storage while the glycemic index reduced from high to low-medium level.     

Drip loss,peroxidase and sensory changes in kiwi fruit slices during frozen storage

The biochemical, sensory and drip loss changes that occur during processing and prolonged frozen storage of kiwi fruit slices (cvs Abbott and Hayward) were studied. Fruit slices were frozen at ?40°C, packed in polyethylene bags and stored at ?18°C for 11 months. Maturity characteristics (pH, acidity, dry matter, soluble solids) were determined on raw fruit. Objective (proteins, peroxidase (EC 1.11.1.7) activity, drip loss) and subjective (sensory tests) analyses were carried out during processing and storage, and indicated a good quality of the frozen kiwi fruit slices after 11 months of storage. There were significant differences (P < 0.05) between the studied varieties with respect to drip loss during frozen storage and colour after 11 months. Best results were obtained with cv Hayward. This variety showed less drip loss after thawing and after 11 months storage presented the same green colour as after freezing, while cv Abbott became yellowish-green.     

Changes in some quality factors of frozen ginger as affected by the freezing storage conditions

The effects of types of ginger root, the freezing storage temperature and time on quality factors associated with color, off‐odor and acceptability of frozen ginger were evaluated to establish the freezing storage conditions of ginger roots. Whole and ground ginger was packed in Nylon/polyethylene (PE) bags and stored at ?5, ?20 and ?40 °C. The quality of the ginger was determined at the following times and storage temperatures: the ginger stored at ?5 °C, ?20 °C, and ?40 °C was sampled at 30‐day intervals for 4 months, at 90‐day intervals for 12 months, and at 120‐day intervals for 16 months, respectively. The content of free sugars, free amino acids (FAAs), unsaturated fatty acids (FUFAs) and volatile compounds noticeably decreased during the storage period, while the total color difference (ΔE) increased, and the temperature effect was significant. The changes in these compounds were generally less in the whole ginger samples. The overall preference of ginger roots stored at ?5, ?20 and ?40 °C was significantly different after 2–3, 9 and 16 months of storage, respectively. The increase of ΔE with decreases of free sugars, FAAs and sensory color indicated the discoloration of frozen ginger was due to the browning reaction. The sensory off‐odor scores were closely associated with the decrease of FUFAs, suggesting that the oxidation of FUFAs caused the development of off‐odor in the frozen ginger. Multiple regression analysis between the overall preference scores and other determined quality factors indicated that FAAs, FUFAs and volatile compounds significantly affected the overall preference scores of ground ginger samples stored at ?5 °C or ?20 °C. The sensory off‐odor and overall preference scores showed that whole ginger could be stored for 2 or 9 months at ?5 or ?20 °C, respectively, maintaining a good overall quality. Copyright © 2006 Society of Chemical Industry     

Kinetic studies on soluble sugar profile in rice during storage: Derivation using the Laplace transform

Soluble sugar is an important parameter to evaluate rice quality during storage. In this study, the changes of soluble sugars (fructose, glucose, maltose and sucrose) in rice during 11 months of storage at 0 °C, 10 °C and room temperature (25 °C) were studied. Laplace transform was applied to solve the models expressed as differential equations based on kinetic changes of soluble sugars during long-term storage. Results showed that the contents of sucrose and maltose in rice decreased whereas fructose and glucose increased over storage time. The soluble sugars in rice showed the best fit to a first-order kinetic model. Furthermore, the rate constants of the soluble sugars at 0 °C were lower than those at 10 °C and room temperature, indicating temperature affected the inter-conversion and degradation of the four soluble sugars, and storage at 0 °C could better delay changes of these sugars in rice during storage.Industrial relevanceKinetic studies on soluble sugars in rice during storage are pretty meaningful due to the complexity of inter-conversion and degradation reactions of the sugars. The present work showed that the developed kinetic model provided a better understanding of the mechanisms of these reactions, and could be used to predict the content changes of soluble sugars in rice during storage.