Quantitative Analysis on 2-Acetyl-1-pyrroline of an Aromatic Rice by Stable Isotope Dilution Method and Model Studies on its Formation during Cooking

A quantitative analysis of 2-acetyl-1-pyrroline from aromatic rice samples using a stable isotope dilution method was developed. The compound was extracted from seedlings, roots, and husks at room temperature for 2 h, whereas milled or brown rice samples were extracted at 75 °C. The recovery of 2-acetyl- 1-pyrroline was linear from 5 to 5000 ng/g with sensitivity of less than 0.1 ng/g. 2-Acetyl-1-pyrroline showed tautomerism with animide form. The results revealed that 2-acetyl-1-pyrroline present in aromatic rice samples did not form during cooking or postharvest processes.     

Activity of ε–Polylysine Against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes

ABSTRACT: ε–polylysine is a homopolymer of L-lysine, an essential amino acid, with a reportedly wide antimicrobial spectrum. This study evaluated the antimicrobial activity of ε–polylysine, as compared with known preservatives and organic acids, against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes , in culture broth. The compounds tested included ε–polylysine (0.0025% to 0.05%), sodium diacetate (0.25%), sodium lactate (3.0%), lactic acid (0.1%), and acetic acid (0.1%), alone, as well as in combination with ε– polylysine (0.0025% to 0.03%); all treatments were evaluated in tryptic soy broth supplemented with 0.6% yeast extract. Treatments were inoculated (approximately 2 log colony-forming units [CFU]/mL) with 5-strain ( E. coli O157:H7, S. Typhimurium) or 10-strain ( L. monocytogenes ) mixtures of the pathogens. Survival/growth of the inoculated bacteria was periodically monitored during incubation at 4 °C (30 d) and 24 °C (48 h). Bactericidal effects of ε–polylysine were obtained against E. coli O157:H7 and S. Typhimurium at 4 °C. At the same temperature (4 °C), ε–polylysine alone or in combination with other compounds tested inhibited growth or was bactericidal against L. monocytogenes. All 3 pathogens were inhibited by ε–polylysine at 24 °C; however, L. monocytogenes was the most sensitive and S. Typhimurium the most resistant. The antimicrobial activity of ε–polylysine against E. coli O157:H7 and S. Typhimurium was enhanced ( P < 0.05) when tested in combination with sodium diacetate or acetic acid. Combination treatments with sodium lactate resulted in loss of ε–polylysine activity by the end of the incubation period. Overall, under the conditions of this study, ε–polylysine exhibited antimicrobial effects against the 3 pathogens tested.     

Starch Retrogradation and Texture of Cooked Milled Rice During Storage

The effect of storing cooked Bengal and Cypress milled rice at -13, 3, 20, and 36 °C on texture and degree of starch retrogradation was investigated. Cooked rice firmness increased, while stickiness decreased, during storage at -13 and 3 °C. Starch retrogradation, measured with a differential scanning calorimeter, was observed for both cultivars during storage at -13 and 3 °C, but not at 36 °C. At 20 °C, retrogradation occurred in Cypress, but not in Bengal. Starch retrogradation showed positive linear trends with firmness for both cultivars at all storage temperatures (R²= 0.80) and with stickiness for Bengal stored at -13 and 3 °C and for Cypress stored at 3 and 20 °C (R2 = 0.88).     

Aroma enrichment and the change during storage of non-aromatic milled rice coated with extracted natural flavor

Three non-aromatic rice varieties (RD23, SPR1 and SPR90) were coated in a modified spouted bed with 30% sorbitol-plasticized rice-starch film containing 25% pandan (Pandanus amaryllifolius Roxb.) leaf extract produced by the supercritical fluid with carbon dioxide extraction method. The coated and uncoated samples and uncoated aromatic rice (KDML and PTT1 varieties) were packed in plastic bags (nylon15/PE20/LLDPE75) and stored at 25 °C for 6 months. Gas chromatography–mass spectrometry analysis revealed that the coating treatment resulted to similar flavor volatile profile as that of aromatic varieties, particularly the presence of 2-acetyl-1-pyrroline (ACPY) which is the main volatile compound responsible for the jasmine aroma. ACPY was absent in uncoated non-aromatic rice and ACPY content of non-aromatic rice coated with natural pandan extract was lower than that of uncoated aromatic rice. During storage, ACPY levels decreased. Coated non-aromatic rice retained higher ACPY levels than the aromatic PTT1 variety. The coating treatment also reduced the n-hexanal content of stored grains. Thus, the coating technique is a promising approach for rice aroma improvement and at the same time, for reducing the potential for oxidative rancidity during grain storage.     

EFFECT OF PROCESSING AND STORAGE CONDITIONS ON THE MICROFLORA OF CLOSTRIDIUM PERFRINGENS-INOCULATED FRANKFURTERS

SUMMARY: The growth support potential of frankfurters for Clostridium perfringens was determined. Inoculated emulsions were stuffed into glass tubes and processed so that they reached an internal temperature of 68–69°C in 30–48 min. The tubes were sealed with agar plugs and rubber stoppers to simulate vacuum-packaging conditions. Total aerobic and anaerobic bacterial counts in uninoculated raw emulsion were 1 to 3 log cycles higher when petri dishes were incubated at 23°C as opposed to 37°C. The low-temperature-growing mesophiles and psychrotrophs were destroyed during processing. The 37°C counts were reduced 1 log cycle and the 23°C counts, 2 to 3 log cycles. Clostridium perfringens reproduced rapidly in frankfurters at 37 and 23°C, more slowly at 15 and 12°C, and not at all during 2 wk of storage at 10° or 4 wk at 0–5°C. Clostridium perfringens made up 2.5–10% of the total anaerobic count at 0 time but became the dominant organism during the storage at all temperatures permitting growth.     

QUALITATIVE AND QUANTITATIVE CHANGES IN AEROBIC MICROFLORA FROM INTESTINAL CONTENTS OF SOUTH-BALTIC COD DURING STORAGE AT 1-2°C

SUMMARY— The bacterial flora of the intestinal content of cod (Gedus morrhua L) were investigated during a period of 1 year. The quantity of bacteria in recently caught fish was studied during the full period. the quality during only 6 months. 3 groups of fish from the same capture and fishing grounds were analyzed: fresh, and stored at 1–2°C for 5 and 10 days. It was seen that in general gram-positive bacterial flora dominated in recently caught fish, while after 5 and 10 days of storage gram-negative flora our numbered the former. In the intestinal contents of fresh fish the Vibrio species dominated, whereas at storage, Pseudomonas spp. became dominant. In fresh fish, the bacterial flora of stored fish amounted to 3.10% of the total initial quantity after 5 days of storage and 1.5% after 10 days. Also, the gram-positive flora decreased comparatively more rapidly than gram-negative flora. The authors believe that the temperature of 1–27°C may play a part in the decreasing number of flora, as well as some other factors not investigated in the present research.     

2-Acetyl-1-pyrroline: A key aroma component of aromatic rice and other food products

2-Acetyl-1-pyrroline is an aroma compound that gives aromatic rice its characteristic flavor. This compound either is present naturally in various food sources or is generated during certain processing methods, as reported in a number of studies. This review focuses on several sources of 2-acetyl-1-pyrroline, including aromatic rice, and the factors, including chemical and genetic parameters, affecting the formation of 2-acetyl-1-pyrroline. Extensive work has been conducted on the agricultural parameters, postharvest processing, storage, and cooking methods, influencing the concentrations of 2-acetyl-1-pyrroline in different food commodities. This article is an attempt to emphasize the importance of this compound in the food industry as a major aroma compound.     

Viscoelastic Changes of Rice Starch Suspensions During Gelatinization

Dynamic rheometry was utilized to characterize viscoelastic changes during heat-induced gelatinization of 2 domestic rice starch suspensions, 1 from waxy and the other from indica rice. Gelatinization included 4 stages: suspension into sol, sol transition to gel, network destruction, and network strengthening. Increase in storage modulus (G') was observed as early as about 47°C. For indica rice, the maximum value (G'_max) was higher, and the decrease afterwards was slower, owing to its higher amylose content. The effects of heating time and temperature were found additive. Sealing samples with oil affected the accuracy of measurement. Finally, the network of starch gels had a larger fractal dimension than that of soy protein isolates previously investigated, suggesting firmer food texture.     

Rheological behaviour of acorn starch dispersions: effects of concentration and temperature

Rheological properties of acorn starch dispersions at different concentrations (4%, 5%, 6% and 7%) were evaluated under steady and dynamic shear conditions. The flow behaviours of the acorn starch dispersions at different temperatures (25, 40, 55 and 70 °C) were determined from the rheological parameters provided by the power law model. The acorn starch dispersions at 25 °C exhibited high shear-thinning fluid characteristics ( n  = 0.23–0.36). Consistency index (K) and apparent viscosity (η_a,100) increased with an increase in starch concentration, and were also reduced with increasing temperature. Within the temperature range of 25–70 °C, the η_a,100 obeyed the Arrhenius temperature relationship with a high determination coefficient ( R ² = 0.97–0.99), with activation energies (E_a) ranging between 16.5 and 19.0 kJ mol⁻¹. Both the power law and exponential type models were employed in order to establish the relationship between concentration and apparent viscosity (η_a,100) in the temperature range of 25–70 °C. Magnitudes of storage ( G' ) and loss ( G ") moduli increased with an increase in the starch concentration and frequency (ω). The magnitudes of G ' were higher than those of G " over most of the frequency range (0.63–62.8 rad s⁻¹). The dynamic (η*) and steady shear (η_a) viscosities of acorn starch dispersion at 7% concentration follow the Cox–Merz superposition rule.     

Charakteristik der Stärke ausgewählter Kartoffelsorten Teil 2. Gehalt an Phosphor,Kalium und Calcium in der Stärke

Characteristics of Starch of Selected Potato Varieties. Part 2. Phosphorus, Potassium and Calcium Content in the Starch . It was found that during storage of potatoes not only changes in starch content and size of the starch granules do occur, but also changes in phosphorus, potassium and calcium content in the starch. The potassium content decreases during storage as a function of temperature. The phosphorus content decreases at +2°C and increases at +10°C. The calcium content increases in the final stage of storage. The phosphorus content in the starch decreases during storage. These results are of special significance with a view to preservation of starch quality.     

INTERRELATIONSHIP BETWEEN CERTAIN PHYSICOCHEMICAL PROPERTIES OF RICE

Water uptake at 80°C and starch-iodine blue value at 65°C, both expressed as percentage of the respective parameter at 96°C gave good inverse estimates of the gelatinization temperature of rice. The equilibrium moisture content on soaking in water was 28–29s in indica , and 30–31% in dwarf indica and japonica rice. Similarly the fraction of total amylose soluble in water (96° C) was around 50% in indica and japonica , but 35% in dwarf indica. Dwarf indica rice viscogram showed a rather high setback value. The blue value of the excess cooking water of rice gave no useful information. Varieties with less than 25% amylose gave C-type alkali reaction.     

Reduction of chilling injury in ripe Alphonso mango fruit in cold storage by temperature conditioning

The influence of ripening temperature and cold conditioning of pre-climacteric fruits on the incidence of chilling injury (CI) in ripe mango fruits cv. Alphonso during refrigerated storage was investigated. Fruits previously held and ripened at tropical ambient temperature (AT, 27–34°C) developed CI (skin staining or browning) when ripe fruits were subsequently stored at 5, 10, or 15°C for shelf-life extension. Fruits held and ripened at 20°C1°C, RH 85–90% showed little evidence of CI when subsequently stored at 5 or 10°C up to 14 days. Chilling injury in ripe mangoes was also avoided by holding pre-climacteric fruits for a minimum period of 30 days at 10°C and then ripening them at 27–34°C. The quality of the ripe mangoes remained good during cold storage for 7 days and were acceptable until 10–14 days with minimal changes in texture, flesh colour, carotenoids, total soluble solids, titratable acids and ascorbic acid. Shelf-life of ripe mangoes can thus be extended under refrigeration by pre-storage conditioning.     

Effects of Na2CO3 and NaOH on Retrogradation of Selected Native Cereal Starches Studied by Differential Scanning Calorimetry and Nuclear Magnetic Resonance

ABSTRACT: Using differential scanning calorimetry and pulsed nuclear magnetic resonance (NMR), it was found that the presence of Na2CO3 and NaOH retarded retrogradation of aged starch (wheat, corn, waxy corn, rice, and waxy rice) gels during storage at 4°C. At the same level of addition (based on a fixed starch/water ratio), the effect of NaOH was observed to be more pronounced than that of Na2CO3. Kinetic studies using pulsed NMR showed a progressive reduction in rate of starch retrogradation with increasing concentration of alkali (up to a level of 1 g/100 starch).     

THE EFFECT OF DEMETHYLATION PROCEDURES ON THE QUALITY OF LOW-ESTER PECTINS USED IN DESSERT GELS

Water uptake at 80°C and starch-iodine blue value at 65°C, both expressed as percentage of the respective parameter at 96°C gave good inverse estimates of the gelatinization temperature of rice. The equilibrium moisture content on soaking in water was 28–29s in indica , and 30–31% in dwarf indica and japonica rice. Similarly the fraction of total amylose soluble in water (96° C) was around 50% in indica and japonica , but 35% in dwarf indica. Dwarf indica rice viscogram showed a rather high setback value. The blue value of the excess cooking water of rice gave no useful information. Varieties with less than 25% amylose gave C-type alkali reaction.     

Purine Content in Grass Shrimp during Storage as Related to Freshness

In grass shrimp ( Penaeus monodon ), the combined total content of the uricogenic bases adenine (Ade) and hypoxanthine (Hyp) decreased gradually during storage. Whether stored at 5°C or at room temperature (22°C), a negative regression of log Ade and a positive regression of the Kp value (Hyp/Ade) were observed. Volatile basic nitrogen (VBN) increased during storage at 5°C and 22°C. Correlations between the content of log Ade and VBN at 5°C and 22°C were –0.9248 (p<0.01) and –0.8139 (p<0.05, while those between the Kp value and VBN were 0.9557 (p<0.001) and 0.8197 (p<0.05), respectively. At the point where the shrimp would remain acceptable, the upper limits of Kp were 1.42 and 1.29 for storage at 5°C and 22°C, respectively; the corresponding lower limits of Ade were 18.72 and 20.42 μmole/g dry wt.     

Cooked and brined shrimps packed in a modified atmosphere have a shelf-life of >7 months at 0 °C, but spoil in 4–6 days at 25 °C

Summary Spoilage and safety of cooked, brined and modified atmosphere packed shrimps were studied at 0, 5, 8, 15 and 25 °C. Shrimps from two sources, cold and warm waters, were brined in a sodium–chloride brine containing benzoic, citric and sorbic acids. Shelf-life was above 7 months at 0 °C but only 4–6 days at 25 °C. Apparent activation energy for the effect of temperature on shelf-life was > 100 kJ mol^-1. This pronounced effect of temperature was explained by changes in spoilage microflora at different storage temperatures. Simple and empirical mathematical models for rates of spoilage were developed for the prediction of shelf-life at different temperatures. To evaluate safety, products were challenged with Listeria monocytogenes and spores of Clostridium botulinum . Above 5 °C growth responses of L. monocytogenes followed the square root model with a T_min-value of +0.2 °C. Cl. botulinum produced toxin at the time of spoilage at 25 °C but only in shrimps with < 3% water-phase salt.     

Effect of Ice Storage on the Physicochemical and Dynamic Viscoelastic Properties of Ribbonfish (Trichiurus spp) Meat

ABSTRACT: Changes in physicochemical and dynamic viscoelastic properties of ribbonfish ( Trichiurus spp) meat during different periods of ice storage were investigated. The differential scanning calorimetry profile of fresh ribbonfish meat revealed transitions at 33.17 °C, 48.85 °C, and 60.96 °C, indicating denaturation temperature of different protein fractions. The effect of cornstarch or tapioca starch at 9% level on the viscoelastic properties of ribbonfish meat stored in ice for different periods was also evaluated. Total volatile basic nitrogen (TVBN) increased significantly ( P < 0.05) during ice storage for 24 d. However, the myosin heavy chain concentration was unaltered during the ice storage period, as revealed by sodium dodecyl sulphate-polyacrylamide gel electrophore-sis (SDS-PAGE) pattern. A significant ( P < 0.05) decrease in protein solubility (in phosphate buffer 50 m M , pH 7.5, containing 1 M NaCl), calcium-activated adenosine triphosphatase (ATPase) activity, and an increase in reduced viscosity at a protein concentration of 5 mg/mL was observed after 10 d of ice storage indicating protein denaturation and aggregation. The addition of tapioca and cornstarch enhanced storage modulus values of fresh ribbonfish meat. The gelatinization temperature of tapioca starch solution was found to be in the range of 60 °C to 65 °C and for cornstarch 67 °C to 70 °C, as revealed by the differential scanning calorimetry (DSC) profile and dynamic rheological testing. The viscoelastic properties of ribbonfish meat was altered significantly ( P < 0.05), both due to the addition of starch and ice storage period as revealed by frequency sweep of prepared gels.     

Texture and other Physicochemical Properties of Whole Rice Bread

ABSTRACT: Samples of experimental rice breads baked in a home bread machine were evaluated by physicochemical methods and compared with a local commercial whole-wheat bread. The results showed that rice breads had less specific volume, harder texture, and were more prone to retrogradation during storage than whole wheat bread. All stored breads showed a peak at about 52 °C by differential scanning calorimetry (DSC) analysis, which is characteristic of retrograded starch. However, the δH for rice bread was about 3 times the value of whole-wheat bread, suggesting its strong tendency to retrograde. X-ray diffraction (XRD) evaluation also indicated the appearance of a strong 20 peak between 16.7 °C to 17.0 °C in rice bread than in whole-wheat bread, which is consistent with starch retrogradation.     

MICROBIOLOGICAL QUALITY OF WHEAT STORED UNDER DIFFERENT CONDITIONS IN TURKEY

Four different types of wheat storage systems are widely used in the Marmara region. The existing storage conditions were studied and changes in the microbiological quality of the stored wheat under these conditions were assessed.
Depending on the external conditions, ambient temperatures and relative humidities in the stores were 17–26°C and 50–65% RH during summer and 3–10°C and 62–83% RH during winter, respectively. The low relative humidity level during harvesting and subsequent storage was adequate for obtaining low levels of moisture content and water activity in the produci for safe storage. The increase in relative humidity of the air during winter months did not affect the moisture content of the product considerably and the low temperature prevented mold growth. Therefore, all of the four different storage facilities were suitable for safe storage of grain for a period of one year without significant losses in quality due to microbiological load.     

The effect of heat treatment on the β-glucosidase activity in canned whole apricots

Summary. Undesirable odour and flavour in canned whole apricots are caused by the products of the β-glucosidase activity in the apricot kernels. the hydrocyanic acid content in canned apricots heat treated for 38 min at 86°C was found to be approximately 1 ppm, with no changes occurring even after long storage; the figure reached a maximum of 16–17 ppm after 150 days of storage at room temperature in fruit heat treated at the same temperature but for only 20 min.