Extraction, partial characterization, and storage stability of β-glucosidase from propolis

Extraction and assay conditions for β-glucosidase from propolis were optimized. Highest enzyme activity was obtained in a citric acid-disodium hydrogen phosphate buffer at pH 6.0 with 2.5% insoluble polyvinylpyrrolidone at incubation temperature of 57 °C. β-Glucosidase activities were found in all freshly harvested propolis while β-glucosidase activities were scarcely present in the randomly bought propolis. Propolis was stored at -20 °C and 4 °C for 3 mo with almost no loss of β-glucosidase activity, but at room temperature the activity decreased exponentially with the increase of storage time. These results indicated that the activity of β-glucosidase could be a candidate for propolis-freshness index. β-Glucosidase from propolis was capable of hydrolyzing p-nitrophenyl-β-D-glucoside and p-nitrophenyl-β-D-galactoside, but lacked activity toward p-nitrophenyl-β-D-glucuronide, p-nitrophenyl-β-D-cellobioside, amygdalin, cellobiose, and gentiobiose. These results were consistent with the hypothesis that flavonoid glucosides were hydrolyzed by β-glucosidase during propolis collection and processing and provided a possible explanation for why some flavonoid biosides (that is, rutin and isorhamnetin-3-O-rutinoside) exist in propolis. Practical Application: β-Glucosidase activity was detected and partial characterization of the enzyme was determined in propolis. The enzyme activity decreased exponentially with the increase of storage time at room temperature, which suggested that the activity of β-glucosidase could be regarded as a freshness index of propolis. The research will be useful for studying the chemical constituents of propolis.     

Activities of calpastatin, μ-calpain and m-calpain are stable during frozen storage of meat

The stability of μ-calpain, m-calpain and calpastatin activity during frozen storage of pork was studied in two experiments. In experiment 1, pork longissimus muscle was stored at either -20 or -80°C, and the samples were assayed at 2-3 weeks interval for calpain activity and calpastatin activity using a m-calpain stock solution stored at 4°C. No effects on calpain activity at either temperature were observed for up to 123 days of storage. Calpastatin activity was stable the first few weeks of storage, where after it decreased up to 143 days of storage independently of meat storage temperature. At day 143, calpastatin activity was also assayed using a newly purified stock solution of m-calpain giving a calpastatin activity equal to the activity measured day 0 using the original m-calpain stock solution. The m-calpain stock solution was unstable during storage at 4°C and the activity decreased in a linear manner and was highly related to the observed decrease in calpastatin activity during storage. In experiment 2, meat was stored as in experiment 1 and was assayed at 2-3week intervals for calpastatin activity using a m-calpain stock solution stored at either 4 or -80°C. As in experiment 1, the measured activity of calpastatin decreased during storage using m-calpain stock solution stored at 4°C and this decrease was highly correlated to the decrease in the activity of the m-calpain stock solution. The activity of the m-calpain stock solution stored at -80°C was constant during storage period of 153 days and likewise was the calpastatin activity measured using this stock solution. The relation between measured calpastatin activity and storage time of m-calpain stock solution was tested by adding, to a calpastatin assay, up to 10μL of a partly inactivated m-calpain solution. A negative relationship was observed between added inactivated m-calpain and measured calpastatin activity which suggests that the inactive m-calpain molecules mask some of the binding sites on calpastatin and thereby prevent some of the active m-calpain molecules from binding to calpastatin. This would underestimate the measured calpastatin activity. In conclusion, the calpains as well as calpastatin are stable during frozen storage of meat, and the observed decreased in calpastatin activity is due to instability of the m-calpain stock solution used in the calpastatin assay.     

Impact of γ-irradiation,CIPC treatment,and storage conditions on physicochemical and nutritional properties of potato starches

In the present study, three potato varieties were treated with chlorpropham (CIPC, 35 ppm), γ-irradiated (0.1 kGy) and stored for up to 5 months at 8 °C, and the physicochemical properties and in vitro starch digestibility of native and cooked starches were investigated. Sprouting was found to be satisfactorily suppressed by γ-irradiation and CIPC treatment. However, irradiation increased total free glucose content in two potato varieties, and decreased the thermal transition and pasting temperature of starch. The crystallinity of starch in irradiated potatoes decreased significantly (p ? 0.05) which may explain its decreased resistant starch content. Sprout inhibiting treatments and storage had no effect on in vitro starch digestibility in cooked starches, but cooling cooked starch significantly (p ? 0.05) increased its resistant starch content.     

Impact of selected factors – Cultivar,storage, cooking and baking on the content of anthocyanins in coloured-flesh potatoes

The impact of selected factors – cultivar, storage, cooking and baking on the content of total anthocyanins (TAC) in coloured-flesh potato cultivars has been studied. TAC ranged from 248.5 to 2257.8 mg kg⁻¹ dry matter (DM). TAC difference between cultivars was statistically significant. Cold storage (4 °C) influenced TAC differentially. In the Violette and Highland Burgundy Red cultivars TAC increased by 18.5% and 12.1% respectively, and in the Valfi cultivar it decreased by 33.9%. Baking increased TAC 3.34 times whereas cooking in boiled water increased it 4.22 times. Correlation between antioxidant activity (AOA) and TAC (r² = 0.659) has been found. The Violette, Vitelotte and Highland Burgundy Red cultivars with the highest TAC showed high AOA and the Shetland Black cultivar and the cultivars Salad Blue and Blue Congo with a “marbled” texture showed the lowest TAC and AOA. Individual anthocyanidins are fingerprints of colour-fleshed potato cultivars.     

Quality of eggs coated with oil–chitosan emulsion: Combined effects of emulsifier types,initial albumen quality,and storage

Effects of mineral oil:chitosan (MO:CH at 25:75) emulsions prepared with four different emulsifiers (2 water- and 2 oil-miscible) as coatings on the internal quality (weight loss, Haugh unit, yolk index, and albumen pH) of coated eggs were evaluated during 5 weeks at 25 ± 2 °C and 20 weeks at 4 ± 2 °C. Eggs with two initial albumen qualities [Haugh unit (HU): H = 87.8 and L = 70.9] were used. At 25 ± 2 °C, Haugh unit, yolk index, and albumen pH of all coated eggs decreased with increased storage time. Coated H- and L-eggs maintained an A-grade up to 4 weeks and 1 week, respectively. Weight loss of all coated eggs remained below 1.35% after 5 weeks of storage at 25 ± 2 °C. All coated eggs maintained an A-grade with less than 2.5% weight loss during 20 weeks of storage at 4 ± 2 °C. Emulsifier types marginally affected the internal quality of coated eggs regardless of storage temperatures.     

Effect of water content,temperature and storage on the glass transition,moisture sorption characteristics and stickiness of β‐casein 1

Moisture sorption isotherms at +4 °C and +22.5 °C were obtained for β‐casein after isolation and after 9 months of storage at ‐29 °C and +22.5 °C. Glass transition state diagrams (T_g vs. moisture) were determined for β‐casein after storage. The results showed that effects of storage temperature on moisture sorption isotherms were varied; however, at any a_w differences in moisture content were small (< 0.03g H₂O/g solids at high a_w). β‐casein stored at ‐29°C had lower m_o and T_g values than that of β‐casein stored at +22.5°C. The glass transition temperatures for β‐casein were above room temperature, even at a_w = 0.76. Onset of stickiness occurred above a_w = 0.76.     

Texture evolution of “Amaretti” cookies during storage

The results of a study on texture evolution during 35 days of storage of amaretti, a typical Italian cookie, packaged in two different ways are reported. Amaretti cookies were wrapped in polyvinylchloride (PVC) film or aluminium foil (ALL), to simulate two different permeability conditions and stored at controlled temperature and humidity. Evolution of texture (such as hardness) and a_w were tested instrumentally by a texture analyser and a hygrometer, respectively. Texture was assessed by a cut and puncturing test. Indices for hardening were the area under the curve (N mm) and gradient (N/mm) for the puncturing test and maximum force (N) for the cut test. Both textural tests showed significantly higher hardening of PVC cookies, compared to the ALL cookies. The latter retained good sensorial properties at the end of the storage period, although their internal structure changed from soft and moist to mealy, while the PVC cookies were no longer edible only 10 days after baking. a_w values decreased and increased in PVC and ALL lots, respectively. The results suggest that hardening may be explained by water loss in PVC and moisture redistribution in ALL.     

Effects of γ-irradiation on Listeria monocytogenes population,colour, texture and sensory properties of Feta cheese during cold storage

Feta, a white brine cheese, was produced and contaminated with Listeria monocytogenes. Contamination occurred either at the beginning (pre-process contamination) or at the end of Feta manufacturing (post-process contamination). In the first case the milk was contaminated with 10³ cfu/ml, and 2 months later, in the final product, the L. monocytogenes population was approximately 10⁵ cfu/g. In the second case, the brine (NaCl, 7% w/v), in which the Feta was packaged, was contaminated with 10³ cfu/ml. Contaminated Feta samples were vacuum-packaged and exposed to irradiation doses of 1.0, 2.5 and 4.7 kGy and stored at 4 °C for a month. In the pre-process contaminated samples none of the irradiation doses eliminated L. monocytogenes; however the highest dose reduced the viable population to a level which is in compliance with EC regulations. In the post-process contamination, the 2.5 kGy and 4.7 kGy doses reduced L. monocytogenes counts below the detection limit. Irradiation had no effect on the texture of Feta. Irradiation at 4.7 kGy increased Feta's redness and decreased its yellowness and lightness. Sensorial analyses showed that at the 4.7 kGy dose, the aroma profile of Feta was temporarily affected, since it was restored after 30 days of cold storage.     

Survival of Salmonella serovars introduced as a post-aging contaminant during storage of low-salt Cheddar cheese at 4, 10, and 21 °C

The microbiological stability of low-salt cheese has not been well documented. This study examined the survival of Salmonella in low-salt compared to regular salt Cheddar cheese with 2 pH levels. Cheddar cheeses were formulated at 0.7% and 1.8% NaCl (wt/wt) with both low and high-pH and aged for 12 wk resulting in four treatments: 0.7% NaCl and pH 5.1 (low-salt and low-pH); 0.7% NaCl and pH 5.5 (low-salt and high-pH); 1.8% NaCl and pH 5.7 (standard-salt and high-pH); and 1.8% NaCl and pH 5.3 (standard-salt and low-pH). Each treatment was comminuted and inoculated with a 5-serovar cocktail of Salmonella at a target level of 4 log CFU/g, then divided and incubated at 4, 10 and 21 °C for up to 90, 90, and 30 d, respectively. Salmonella counts decreased by 2.8 to 3.9 log CFU/g in all treatments. In the initial period of survival study, standard-salt treatments exhibited significantly lower Salmonella counts compared to low-salt treatments. The pH levels did not exhibit obvious significant effect in the Salmonella survival in low-salt treatments. Salmonella counts declined gradually regardless of a continuous increase in pH (end pH of 5.3 to 5.9) of low-salt treatments at all study temperatures. Salmonella counts were reduced faster at 21 °C storage. Although there were significant reductions in Salmonella counts, the treatments demonstrated survival of Salmonella for up to 90 d when stored at 4 or 10 °C and for up to 30 d at 21 °C, the need for good sanitation practices to prevent postmanufacturing cross contamination remains. PRACTICAL APPLICATION: Low-salt aged Cheddar cheese could not support the growth of inoculated Salmonella and in fact gradual reduction in Salmonella count occurred during storage. Besides being nutritionally better, low or reduced salt Cheddar are safe as their full salt counterparts and that salt may only be a minor food safety hurdle regarding the post-aging contamination and growth of Salmonella. However, the treatments could not demonstrate complete destruction of Salmonella for up to 90 d when stored at 4 or 10 °C and for up to 30 d at 21 °C, the need for good sanitation practices to prevent postmanufacturing cross-contamination remains.     

Effects of dietary α-linolenic acid on the fatty acid composition, storage stability and sensory characteristics of pork loin

Effects of dietary α-linolenic acid on the fatty acid composition, storage stability and sensory characteristics of cooked pork were studied. Dietary α-linolenic acid (LNA) significantly (p < 0.05) increased the proportion of n−3 fatty acids and the degree of unsaturation in the neutral lipids and phospholipids. The increases in n−3 fatty acids were observed in the total lipids, triglycerides, phosphatidylethanolamine and phosphatidylcholine, and mainly consisted of C18:3n3, C20:5n3 and/or C22:5n3.The thiobarbituric acid reactive substances (TBARS) values (mg malondialdehyde per kg meat) of cooked vacuum packaged loins remained below 1.5, but in loose packaged loins TBARS values increased more than 3 times those of 0 time values during 2-day storage at 4 °C. The TBARS values of loins after LNA-enrichment were significantly higher than those of the control in both vacuum and loose packaging, and the increase of unsaturation in fatty acids had a strong prooxidant effect. The increase in dietary LNA enrichment increased oxidation (TBARS values) and had a detrimental effect on the acceptability of cooked pork loins held for 2 days in loose packaging.     

Survival of Listeria monocytogenes introduced as a post-aging contaminant during storage of low-salt Cheddar cheese at 4, 10, and 21°C

Traditional aged Cheddar cheese does not support Listeria monocytogenes growth and, in fact, gradual inactivation of the organism occurs during storage due to intrinsic characteristics of Cheddar cheese, such as presence of starter cultures, salt content, and acidity. However, consuming high-salt (sodium) levels is a health concern and the dairy industry is responding by creating reduced-salt cheeses. The microbiological stability of low-salt cheese has not been well documented. This study examined the survival of L. monocytogenes in low-salt compared with regular-salt Cheddar cheese at 2 pH levels stored at 4, 10, and 21°C. Cheddar cheeses were formulated at 0.7% and 1.8% NaCl (wt/wt) with both low and high pH and aged for 10 wk, resulting in 4 treatments: 0.7% NaCl and pH 5.1 (low salt and low pH); 0.7% NaCl and pH 5.5 (low salt and high pH); 1.8% NaCl and pH 5.8 (standard salt and high pH); and 1.8% NaCl and pH 5.3 (standard salt and low pH). Each treatment was comminuted and inoculated with a 5-strain cocktail of L. monocytogenes at a target level of 3.5 log cfu/g, then divided and incubated at 4, 10, and 21°C. Survival or growth of L. monocytogenes was monitored for up to 90, 90, and 30 d, respectively. Listeria monocytogenes decreased by 0.14 to 1.48 log cfu/g in all treatments. At the end of incubation at a given temperature, no significant difference existed in L. monocytogenes survival between the low and standard salt treatments at either low or high pH. Listeria monocytogenes counts decreased gradually regardless of a continuous increase in pH (end pH of 5.3 to 6.9) of low-salt treatments at all study temperatures. This study demonstrated that post-aging inoculation of L. monocytogenes into low-salt (0.7%, wt/wt) Cheddar cheeses at an initial pH of 5.1 to 5.5 does not support growth at 4, 10, and 21°C up to 90, 90, and 30 d, respectively. As none of the treatments demonstrated more than a 1.5 log reduction in L. monocytogenes counts, the need for good sanitation practices to prevent post-manufacturing cross contamination remains.     

MRI ‘texture’ analysis of MR images of apples during ripening and storage

Images obtained by magnetic resonance imaging (MRI) of the apple varieties Idared, Redspur and Topaz during ripening and storage were analysed by texture analysis (TA) to determine the correlation between TA parameters and firmness, soluble solids content (SSC) and titratable acids. All varieties differ significantly in SSC, acidity and the firmness of fruits. Three sagital T2w slices measured at 4.7 T (resolution 256×256 pixels) were analysed numerically using the software MaZda 2.11 and the statistical package S-PLUS 4.5. A significant correlation was found between acidity and TA parameters such as sum average, sum variance and sum entropy. The dynamics of TA parameters during the periods of maturation and storage were described by polynomial functions.The following distinctive TA parameters were found: skewness and kurtosis (among histogram-based parameters), variance of absolute gradient (among gradient-based parameters), grey level nonuniformity (among run length matrix-based parameters) and especially some co-occurrence matrix-derived parameters such as correlation, sum average, sum variance and sum entropy (within 1-, 3-, and 5-pixel neighbourhoods). The TA parameter correlation obtained from MR images can be used for characterising fruit ripening.     

Effects of marination, cooking and storage on physico-chemical and microbiological properties of ready to eat trout döner kebab

The aim of this work was to investigate the use of rainbow trout (Oncorhynchus mykiss) in ready to eat döner kebab production and determine the effects of marination, cooking and storage conditions (4 and ?18 °C) on physico-chemical and microbiological properties of döner kebab. The raw trout meat, raw, cooked and stored döner kebab samples were subjected to moisture, protein, fat, ash, color, pH, cholesterol, biogenic amines, lipid oxidation, fatty acids profile, texture, microbiological and sensory analysis. The results indicated that the major fatty acids in trout döner kebab were palmitic, stearic, oleic, omega-3 and omega-6 fatty acids and unsaturated fatty acids were higher than saturated fatty acids (p < 0.05). Low biogenic amine and cholesterol contents were determined in döner kebab. It was found that ?18 °C of storage temperature was more effective than 4 °C for inhibition of lipid oxidation and microbial growth in trout döner kebab (p < 0.05). While cooking affected parameters evaluated (p < 0.05), marination did not have any significant effect. The study results indicated that using rainbow trout meat in döner kebab production could be beneficial to provide healthy meat products without posing any acceptability problems in terms of quality factors. This is the first paper to be reported on physico-chemical and microbiological properties of döner kebab produced with rainbow trout and effects of marination, cooking and different storage temperatures on these physico-chemical and microbiological properties.     

Effect of rosemary extract, chitosan and α-tocopherol on lipid oxidation and colour stability during frozen storage of beef burgers

The effect of rosemary extract, chitosan and α-tocopherol, added individually or in combination, on lipid oxidation and colour stability of frozen (−18 °C) beef burgers stored for 180 days was investigated. The burgers’ lipid oxidation and appearance were evaluated through measurement of primary (conjugated dienes and peroxide value) and secondary (malondialdehyde) oxidation products, together with visual assessment and instrumental measurement of colour. Chitosan alone and in combination with either rosemary or α-tocopherol had the best antioxidative effect (P ? 0.05) compared to individual use of rosemary or α-tocopherol, while the best results were obtained with the combination of chitosan and rosemary. The differences of antioxidative effects, however, between individual use of rosemary or α-tocopherol as compared to the controls were also significant (P ? 0.05). Chitosan added individually or in combination with either rosemary or α-tocopherol had also a noteworthy effect on the burgers’ appearance as it contributed to red colour retention for a much longer period (P ? 0.05) compared all other treatments and the controls. In conclusion, the best antioxidative effects were obtained with the combination of chitosan and rosemary extract.     

Influence of γ-irradiation on the reactive-oxygen metabolism of blueberry fruit during cold storage

To explore a safe, environmentally friendly, and efficient preservation technology for blueberry (Semen trigonellae), “Bluecrop” blueberry fruits were treated with different irradiation doses. During cold storage at 0 ± 5 °C, the decay rate, fruit firmness, and indices relating to respiration and reactive-oxygen metabolism were detected regularly. Results showed that irradiation treatment with 1.0 kGy to 2.5 kGy doses was able to inhibit the respiration intensity, ethylene production, and the improvement of lipoxygenase (LOX) activity, thus reducing the increase of malondialdehyde (MDA) content and the permeability of cell membranes. In addition, irradiation treatment can improve the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) to eliminate, on a continual basis, the constantly generated superoxide anions (O₂⁻) and hydrogen peroxide (H₂O₂), keeping them at a low level: ultimately, this effectively guaranteed the storage quality and postponed the senescence process in the blueberry fruits. Meanwhile, those irradiated at 2.5 kGy presented optimal preservation effects as the respiration was inhibited to the utmost extent and the anti-oxidisation effect was enhanced. The results prove that the ⁶⁰Co γ-irradiation treatment at proper doses is an effective method of storing post-harvest blueberry fruits at low temperatures.     

Physio-chemical behavior of γ-irradiated garlic bulbs under ambient storage conditions

The present study was undertaken to study the effect of different gamma irradiation doses on storage life of garlic bulbs under ambient storage conditions. Garlic bulbs (cv. PG-18) were irradiated with gamma rays in dose range of 0–0.2 kGy and stored under ambient conditions (Temp 27–35 °C and RH 34–76%). Physical and chemical quality parameters i.e. physiological loss in weight (plw), rotting, sprouting, total soluble solids, firmness, ascorbic acid and allicin content of garlic bulbs was determined fortnightly to assess its storage life. On 195th day of ambient storage, the weight loss of bulbs ranged from 32.22 to 38.48% in all irradiation doses. It was observed that upto 30 days and 150 days, there was no rotting and sprouting, respectively in all the treatments. Firmness, total soluble solids, ascorbic acid and allicin content were significantly different with storage period and irradiation dose levels. It is concluded that garlic bulbs irradiated @ 0.12 kGy of gamma radiation resulted in minimum post-harvest losses along with maintaining their marketable shelf life for 4 months under ambient storage conditions.     

The influence of storage on aroma, soluble solids, acid and colour of sour cherries (Prunus cerasus L.) cv. Stevnsbær

The present study involved a laboratory scale experiment where the impact of post-harvest storage on the quality of sour cherries (Prunus cerasus L.) cv Stevnsbær was investigated. Cherries were stored for 7 days at temperatures of 2??°C, 10??°C, 20??°C, and 30??°C, and at 20??°C in combination with a 20% CO₂ atmosphere. Cherry quality was assessed by analysis of soluble solids, titrateable acids, anthocyanins and aroma compounds. The content of soluble solids of cherries decreased at storage temperatures above 10??°C. The anthocyanin content of cherries decreased during storage at all temperatures. A decrease, followed by an increase, in titrateable acid was observed for all temperatures except 2??°C. Aroma components were also affected by storage time and temperature. The level of benzaldehyde decreased during storage at higher temperatures, while those of eugenol and vanillin increased at all temperatures. The levels of "off" odour compounds, like acetic acid and fermentation alcohols, increased at higher temperatures during storage. The CO₂-enriched atmosphere (20%?CO₂) did not affect the different quality factors significantly.     

Lipid and protein oxidation, release of iron from heme molecule and colour deterioration during refrigerated storage of liver pâté

In the present work, lipid and protein oxidation, increase of non-heme iron (NHI) content and colour changes occurring during refrigerated storage (90 days/4 °C) of liver pâtés from Iberian and white pigs were studied. Iberian pigs were reared outdoors and fed on natural resources (grass, acorns) while white pigs were intensively reared and fed on a mixed diet. Lipid and protein oxidation were, respectively, measured by determining TBA reactive substances (TBARS) and protein carbonyl groups. Pâtés from Iberian pigs had better oxidative stability at all stages of storage, having lower amounts of TBARS and carbonyls compared to those from white pigs (p<0.05). NHI increased during refrigerated storage of liver pâtés, with those from white pigs having a higher amount of NHI at all stages of storage (p<0.05). During refrigerated storage, L^*-values tended to increase while the evolution of a^* and b^* depended on the group and did not seem to be related to the oxidative processes.