Process stability of Capsicum annuum pectin methylesterase in model systems, pepper puree and intact pepper tissue

Process stability studies towards temperature and/or pressure on pepper pectin methylesterase (PME) were carried out in different systems (purified form, crude extract, pepper pieces and puree) at pH 5.6. Within the temperature range studied (22–80 °C, 5 min), pepper PME in pure form and crude extract was gradually inactivated showing a biphasic inactivation behaviour, indicating the presence of isoenzymes of different thermostability. Pepper samples heated for 15 min showed a maximum of residual PME activity around 55 °C. Isothermal inactivation of pepper PME in purified form and crude extract at pH 5.6 could be described by a biphasic inactivation model for the temperature range studied (62–76 °C). A stable behaviour towards high-pressure/temperature treatments (400–800 MPa/25–60 °C) was observed for crude extract and purified pepper PME. PME in pepper puree samples revealed to be very pressure stable. Mild temperatures combined with pressure treatments seem to increase the extractability from PME in pepper tissue, probably due to the effect on the cell structure.     

Effect of temperature and modified atmosphere packaging on overall quality of fresh-cut bell peppers

The effect of vacuum packaging (VP) and modified atmosphere packaging without vacuum (MAP) on shelf-life of fresh-cut green bell pepper stored at 5°C and 10°C were evaluated. In-package atmosphere, overall quality, percentage of leaked juice, texture, ascorbic acid content, ethanol and acetaldehyde, and microbial growth, were evaluated at different intervals of storage. MAP-fresh-cut peppers presented better visual quality, less leaked juice and higher firmness than those stored under VP. Microbiological and quality analysis revealed a limit of shelf-life of 14 and 21 days, when fresh-cut peppers were stored at 10°C and 5°C, respectively. We conclude that MAP could be used to maintain quality attributes of fresh-cut peppers for up 21 days at 5°C.     

Effect of thermal blanching and of high pressure treatments on sweet green and red bell pepper fruits (Capsicum annuum L.)

The effect of pressure treatments of 100 and 200 MPa (10 and 20 min) and of thermal blanching at 70 °C, 80 °C and 98 °C (1 and 2.5 min), on sweet green and red bell peppers was compared. Pressure treated peppers showed a lower reduction on soluble protein and ascorbic acid contents. Red peppers presented even an increased content of ascorbic acid (15–20%), compared to the untreated peppers. Peroxidase and pectin methylesterase (whose activity was only quantifiable in green peppers) showed a higher stability to pressure treatments, particularly the latter enzyme, while polyphenol oxidase was inactivated to the same final level by the thermal blanching and pressure treatments. Pressure treatments resulted in comparable (in green pepper) to higher (in red pepper) microbial loads compared to blanching. Pressure treated green and red peppers presented similar to better firmness before and after tunnel freezing at −30 °C, compared to thermally blanched peppers, particularly those blanched at 98 °C. The results indicated that pressure treatments of 100 and 200 MPa can be used to produce frozen peppers with similar to better nutritional (soluble protein and ascorbic acid) and texture (firmness) characteristics, comparable activity of polyphenol oxidase and higher activity of pectin methylesterase, while pressure treated peppers show a higher level of peroxidase activity. It would be interesting to use higher pressures in future studies, as an attempt to cause a higher reduction on microbial load and on enzymatic activity.     

Effect of hot-air drying on flavour compounds of bell peppers (Capsicum annuum)

The influence of hot-air drying on the composition of both volatile and non-volatile flavour compounds of different Dutch bell pepper cultivars was investigated. Contents of glucose, fructose, ascorbic, citric, and oxalic acid decreased significantly after drying, while the levels of sucrose, malic, fumaric, and cis-aconitic acid increased. Glucose, fructose and ascorbic acid probably participate in Maillard reactions during heating. Different effects of drying could be distinguished on the composition of volatile compounds. The majority of these compounds evaporated during drying. Some compounds were partly retained in the dried bell peppers, whereas others disappeared completely. Gas chromatography-sniffing port analysis revealed that compounds with mainly “fresh” odour notes like lettuce/grassy/green bell pepper ((Z-2-3-hexenal), fruity/almond ((E)-2-hexenal), fruity (octanal), lettuce/green bell pepper ((Z)-3-hexenol), and grassy/green bell pepper ((Z)-2-hexenal) decreased or disappeared after drying. Another group of compounds increased or were formed during drying, like 4-octen-3-one, (E)-2-heptenal, (E)-2-octenal, (E,Z)- and (E,E)-2,4-heptadienal, decanal, and (E)-2-nonenal; most are known as autoxidation products of unsatu-rated fatty acids. The increased levels of 2-methylpropionic and 2- and 3-methylbutyric acid, 2-metlhylpropanal, and 2- and 3-methylbutanal seemed to be due to Strecker degradation. Gas chromatography-sniffing port analysis showed that the latter three compounds had distinct cacao, sweaty, and spicy odour characteristics.     

Effect of mild pressure treatments and thermal blanching on yellow bell peppers (Capsicum annuum L.)

The effect of thermal blanching, in conditions carried out at industrial level, and pressure treatments of 100 and 200 MPa on quality of yellow bell peppers was compared. While the soluble protein content was reduced from 13 to 34% by the blanching treatments, the pressure treated peppers showed equal (100 MPa) to higher levels (up to 33%) for 200 MPa. The ascorbic acid (AA) content of the peppers was not affected by thermal blanching, with the exception of the more severe condition (98 °C/150 s), whereas all pressurized samples showed an increase of AA content in the range of 11-48%. Polyphenol oxidase activity was found mainly in the soluble fraction (around 80%) and decreased progressively as the temperature and time of blanching increased, till reaching about 50% the value of unprocessed peppers, while the pressure treatments showed no effect. Peroxidase activity was practically absent in the ionically-bound fraction (only 1% of total activity) and was reduced by the blanching treatments by 80%-100%, while the pressure treatments only reduced peroxidase activity from 5 to 10%. Activity of pectin methylesterase was undetectable in fresh and both thermally and pressure processed peppers. Firmness of peppers measured from the skin side was about 2.5 fold higher than from the flesh side. After the thermal blanching and the pressure treatments, firmness of peppers was better retained when measured from the flesh side. Upon freezing the pressure treated and the thermally blanched peppers showed similar relative decreases in firmness.     

Minimizing texture loss of frozen strawberries: effect of infusion with pectinmethylesterase and calcium combined with different freezing conditions and effect of subsequent storage/thawing conditions

Vacuum infusion (VI), freezing, frozen storage and thawing conditions were optimized in order to minimize the texture loss of frozen strawberries. Slow freezing caused severe loss in textural quality of the strawberries. This quality loss could not be prevented by the application of VI prior to slow freezing, or by the application of rapid, cryogenic or high-pressure shift freezing conditions on non-infused fruits. A remarkable texture improvement was noticed when infusion of pectinmethylesterase (PME) and calcium was combined with rapid or cryogenic freezing. The highly beneficial effect of PME/Ca-infusion followed by HPSF on the hardness retention of frozen strawberries was ascribed to the combined effect of the infused PME (53% reduction in degree of esterification (DE) of the strawberry pectin) and the high degree of supercooling during HPSF. During frozen storage, textural quality of PME/Ca-infused high-pressure frozen strawberries was maintained at temperatures below −8 °C, whereas the texture of PME/Ca-infused strawberries frozen under cryogenic freezing conditions was only preserved at temperatures below −18 °C. Thawing at room temperature seemed to be an appropriate method to thaw strawberries. Fast thawing by high-pressure induced thawing (HPIT) did not prevent textural quality loss of frozenstrawberries.     

Synergy between high-pressure, temperature and ascorbic acid on the inactivation of Bacillus cereus

B. cereus strain (CECF 148) was used as a model system in the study of the behaviour of bacillus under high pressure, at temperatures over and below 0 °C and with ascorbic acid added to the culture. Three different assays were carried out in the present experiment. The first assay was performed to observe how B. cereus reacted to pressure shift freezing (PSF) treatment at different subzero temperatures (−8, −12, −20 and −17 °C) and pressures (120, 150, 210 and 350 MPa) in their vegetative form. In the second assay, we observed how different concentrations of ascorbic acid (1, 2, 5 and 20 mM) added to the growing brought decreased B. cereus on its vegetative form. Finally, we tried to inactivate the vegetative and spore form of B. cereus under pressure of 210 MPa at room (20 °C) (HP) and at subzero (−20 °C) (PSF) temperatures, in presence of ascorbic acid (20 mM), added to the growing culture (TSB). The results confirmed that pressures of 210 and 350 MPa at low temperatures (−20 and −17 °C) in the PSF treatment were not enough to inactivate bacillus and only about 10% of B. cereus at the assayed conditions (350 MPa at −17 °C) lost its growth capacity. The presence of ascorbic acid reduced the amount of B. cereus. The initial amount of B. cereus in the vegetative form was 10⁸ to 10⁹ cfu/mL. After HP (210 MPa at 20 °C) and PSF (210 MPa at −20 °C) treatments, the amount of B. cereus decreased by 4 and 2 logarithmic units, respectively. However, in both treatments, the presence of ascorbic acid (20 mM concentration) reduced the B. cereus growth capacity in about 5 logarithmic units. The presence of ascorbic acid in the spore form decreased the amount of B. cereus only by 2 logarithmic units, but without the antioxidant, the values remained close to control. The present research is a contribution to elicit the safety standards of food treated by high pressure.     

The effect of the pre-treatments and the long and short-term frozen storage on the quality of raspberry (cv. Heritage)

Results are presented of the effect of pre-treatments before freezing followed by long and short-term frozen storage (12 months at –18 °C and 24 days suffering temperature fluctuations between –18 °C and –12 °C) on quality parameters of raspberry. Pre-treatments were carried out with calcium, low methoxyl pectin, a combined solution, and results compared with untreated control fruits. Kramer shear, back extrusion, compression, and multiple penetration tests were used to measure rheological behavior. One-hundred mM CaCl₂ reduced the long and short-term frozen storage induced loss of firmness. For long-term storage at –18 °C, a softening of the tissue became evident between 3 and 12 months and at each date test the stored fruits were firmer than those without storage. For short-term storage with fluctuations, the loss of firmness was evident between 0 and 24 days, and at all the testing dates the stored fruits were softer than those without storage. Results evidenced a higher cell damage in the short-term frozen storage. Coefficients of softening per day suffering fluctuation were determined, the highest values being given by Kramer shear energy and back extrusion maximum force (>1%). Short-term frozen storage affected physical and physico-chemical characteristics, increasing the saturation (r) and the anthocyanins and decreasing the ascorbic acid of the raspberries. In both storage conditions, pre-treatments reduced the drip loss, which correlated best with the Kramer shear energy. Panelists detected mainly time effect on the sensory firmness. For long-term, sensory firmness and juiciness gave the highest correlations with back extrusion maximum force, while for the short-term, sensory firmness and drip loss gave the highest correlations with the Kramer shear energy. SEM revealed different degrees of mechanical damage to structure, which accounted for rheological behavior of the fruits.     

Effects of Kudoa spores,endogenous protease activity and frozen storage on cooked texture of minced Pacific hake (Merluccius productus)

The effects of Kudoa infection of Pacific hake (Merluccius productus) on endogenous protease activity and on cooked mince texture were investigated. Texture was significantly (p < 0.05) negatively correlated with spore counts as well as protease activity. Soft texture (maximum force <150 g) was observed in fish with 10⁴–10⁶Kudoa thyrsites spores g⁻¹ mince, compared to 10⁵–10⁸K. paniformis spores g⁻¹ mince, suggesting that especially for fish having lower infection levels, K. thyrsites may have a greater impact than K. paniformis on Pacific hake quality. Pre-incubation for 15 min at 52 °C prior to cooking resulted in softer texture in some samples due to endogenous proteolytic action. This pre-incubation effect was not consistently observed in fish held 6 months or longer at −25 °C or after freeze-thaw cycling, which may be explained by an opposing toughening effect attributed to protein denaturation and aggregation during prolonged or abusive frozen storage.     

Monte Carlo Simulation to establish the effect of pH, temperature and heating time on the final load of Bacillus stearothermophilus spores

Bacillus stearothermophilus heat treatment studies at different pH levels were carried out in order to predict the final microbiological load as affected by the temperature and pH treatment. For that, distribution functions were obtained for the initial number of microorganisms, the decimal reduction coefficient, the z _T and the z _pH parameters, and Monte Carlo Simulation was used as a tool to determine this microbial load after a heat treatment introducing in this way the variability and uncertainty. The mean value of the predictions made by Monte Carlo Simulation, when compared with independent data, rendered Accuracy Factors close to 1, values close to 1 indicated good predictions. Bias values were close to 1, but some values were below 1 and others above 1. The tornado graphs indicated that the main factor contributing to the final load after the heat treatment was the initial number of microorganisms followed by the temperature and pH.     

Blanching effects on chemistry, quality and structure of green beans (cv. Moncayo)

Green beans (cv. Moncayo) were blanched at 65, 70, 75, 80, 85, 90 and 97 °C for 2.5, 5, 10, 20 and 40 min. Pectinesterase (PE) activity was highest in cell-wall-bound extracts of beans blanched at 70 °C/10 min. The lowest water-soluble pectin fraction, the highest EDTA-soluble pectin fraction and the lowest degree of esterification of the EDTA-soluble fraction were all recorded for the same temperature/time combination; these effects can therefore be attributed to PE activity. Chemical changes did not affect initial firmness of the beans, which was practically constant after blanching at 65, 70, 75 and 80 °C. Simple first-order models were adequate to establish softening kinetics for beans blanched at 85, 90 and 97 °C. In this temperature range, Kramer maximum force was the mechanical parameter that best characterised bean softening by blanching. For all temperatures, short-time blanching increased the coloration and total chlorophyll content of the samples with respect to fresh control, thus precluding the use of simple models. In the treated beans, the ascorbic acid content was consistently lower than in the control and decreased continuously with increasing time. Microphotographs showed no appreciable differences in morphology between fresh and blanched beans at 65, 70 and 75 °C, which would explain the similarity of mechanical behaviour in these samples. Blanching at 85, 90 and 97 °C caused loosening and swelling of the cell walls owing to breakdown of the pectic material, which again helps to explain the observed loss of firmness.     

Effect of phytic acid degradation by soaking and exogenous phytase on the bioavailability of magnesium and zinc from Pisum sativum, L.

The effect of dephytinization of Pisum sativum, L. flour on the bioavailability of Mg and Zn was evaluated in growing rats. Processing of legume flours under optimal conditions for phytase activity (pH 5.5, 37 °C, 60 min) and subsequent removal of the soaking solution led to a 42 and 61% reduction in the content of Mg and Zn, respectively. Treatment with phytase led to an additional reduction in the concentration of the above-mentioned seed flour components, compared to the raw pea flour (69% and 74% for Mg and Zn, respectively). The considerable reduction in the content of inositol phosphates with high degree of phosphorylation attained under both processing conditions did not affect the digestive utilization of Mg, whereas the metabolic utilization of this mineral increased significantly. The digestive and metabolic utilization of Zn increased significantly in response to both processes assayed, reaching the highest values in the experimental group that was fed the phytase-treated pea flour diet. The amount of Mg retained by the experimental animals was reflected in the content of this mineral in the different tissues studied (femur, sternum, kidney, and heart), whereas no correlation was found in the case of Zn.     

Effect of pulsed vacuum and ultrasound osmopretreatments on glass transition temperature, texture, microstructure and calcium penetration of dried apples (Fuji)

The effect of pulsed vacuum and ultrasound pretreatments on glass transition, texture, rehydration, microstructure and other selected properties of air- and freeze-dried apples (Fuji) were investigated. Apple cylinders (15 mm height × 15 mm diameter) were first osmoconcentrated in a 60 g/100 g high-fructose corn syrup solution containing 7.5 g/100 g Gluconal Cal^® combined with agitation, pulsed vacuum (PV), or ultrasound for 3 h, then hot-air or freeze dried. Changes in glass transition temperature, hardness, crispness, and rehydration rate were measured, microstructure was observed using scanning electronic microscopy (SEM), and calcium ions distributions were analyzed by a laser ablation inductively coupled mass spectrometry (LA-ICP-MS). Under the same drying method, ultrasound led to a higher glass transition temperature, lower water activity, moisture content and rehydration rate, severer structure collapse, less cavities and calcium uptake than PV did. Different osmoconcentration pretreatment had no significant (P < 0.05) effect on the hardness, crispness, shrinkage and rehydration rate. Compared to hot-air drying, freeze-dried apples showed the porous structure, minimal shrinkage, softer texture, better rehydration capacity, lighter color, and slightly lower glass transition temperature.     

Effect of high pressure, temperature, and storage on the color of porcine longissimus dorsi

The color of pork longissimus dorsi high pressure (HP) treated at 200 to 800MPa at 5 and 20°C for 10min was determined to a high degree by pressure level and to a lesser degree by temperature. Severe color changes appeared up to a threshold pressure at 400MPa. HP treatment at 20°C compared to 5°C resulted in meat, which was less red and slightly lighter. Storage at 2°C for 6days had no effect on lightness due to no further protein denaturation, but meat HP treated above 300MPa became significantly less red and more yellow within the first day of storage. Reflectance spectra showed that a short-lived ferrohemochrome myoglobin species was formed during HP treatment at 300 to 800, but transformed into a brown, ferric form of the pigment within the first day of storage. This explains the observed changes in the redness and yellowness after one day of storage.     

Effect of temperature on the life cycle of Aleuroglyphus ovatus (Acari: Acaridae) at four constant temperatures

The effect of four constant temperatures (20, 24, 28 and 32 °C) on the physiological properties (survival, developmental time, sex ratio, fecundity and longevity of females), and population growth of Aleuroglyphus ovatus was examined in the laboratory at 85% relative humidity. The total developmental time, longevity and oviposition period of A. ovatus shortened as temperature increased. The shortest developmental time (14.70 ± 0.34 days) was obtained at 32 °C. At 20, 24, 28 and 32 °C, mated females laid on average 0.87 ± 0.10, 2.57 ± 0.13, 3.14 ± 0.27 and 1.29 ± 0.16 eggs per day, respectively. Maximum fecundity was recorded at 28 °C with 70.83 ± 10.16 eggs per female. The highest intrinsic rate of increase (r_m) was found to be 0.16 at 28 °C.     

Freezing, thawing and cooking effects on quality profile assessment of green beans (cv. Win)

Results are presented of the effect of freezing followed by thawing (air and water immersion, both at environmental temperature) and cooking (traditional boiling in a covered pot) on quality profile (in terms of objective texture, colour, chlorophylls and pheophytins and sensory attributes) and structure of green beans (cv. Win). Freezing was carried out at three different rates by forced convection with liquid nitrogen vapour. Kramer shear cell (KSC) and Warner–Bratzler (WB) tests were used for objective assessment of the texture. The highest parameter values occurred in beans frozen at the highest rate and air-thawed at the slowest rate. Also, minimum alteration of the rheological behaviour of cooked beans was achieved by freezing at the highest rate. The best parameter for assessing the texture of frozen green beans after thawing and cooking was the Warner–Bratzler slope (S _WB). Coefficients of softening estimated for S _WB in the thawed beans showed that the texture of the beans frozen at −24 °C was almost four and almost five times softer than that of the beans frozen at −70 °C, for air and water thawing respectively. Frozen and thawed green beans were darker than fresh control, whereas freezing prior to cooking produced lighter-coloured beans than direct cooking. The freezing rate affected colour parameters differently depending on the process that followed. When beans were thawed, increasing the freezing rate produced lighter-coloured beans, whereas when beans were cooked, increasing the rate produced darker-coloured beans. No difference was found in sensory assessments between cooked samples frozen at −24 °C, −35 °C and −70 °C, which probably reflects the panellists' mixed preferences for quickly and slowly frozen samples. Scanning electron microscopy (SEM) revealed different degrees of mechanical damage to tissue structure, which accounted for the rheological behaviour of the beans.     

Effect of high pressure on K-value, microbial and sensory characteristics of yellowfin tuna (Thunnus albacares) chunks in EVOH films during chill storage

The effect of different high pressure treatments on K-value, total plate count, enterobacteriaceae and organoleptic characteristics of yellowfin tuna chunks packed in ethyl vinyl alcohol (EVOH) films during chill storage (2 ± 1 °C) was studied. 50 g of fresh tuna chunks were placed in EVOH multilayer film pouches and vacuum packed for the trials. Tuna chunks were subjected to 100, 200 and 300 MPa for 5 min at 25 °C. Control was vacuum packed tuna without pressure treatment. K value, microbiological analysis and sensory characteristics were evaluated at periodic intervals. The K-value of the samples was found to decrease with increase in pressure when compared to the control. However, K-value was found to increase in all the samples during storage. Higher pressure treatment showed a decrease in the total plate count in the samples which increased during the storage. The Enterobacteriaceae decreased with increasing pressure and during storage. Control samples were sensorally acceptable up to 20 days of storage. During the storage period of 30 days 200 MPa treated tuna chunks was found most acceptable based on above parameters.

Industrial relevance

High pressure processing is a non thermal processing method which has wide applications in food industry. Fish is a highly perishable commodity and it has a limited shelf life in chill conditions. High pressure treatment has been found to effectively extend the shelf life of various products. In this study, HPP has been effectively demonstrated for enhancing the storage period of tuna at low temperature. Such studies can be commercially applied by fish processing industries to preserve the valuable catch and can enhance the marketing potential of tuna.     

Effect of cooking temperature and time on the physico-chemical, histological and sensory properties of female carabeef (buffalo) meat

The effect of cooking temperature (80-100°C) and time (30-60min) on collagen solubility of Semimembranosus muscle in carabeef were investigated. The pH, cooking loss, shear force value, collagen content, collagen solubility, sensory evaluation and histological observations of water bath cooked and pressure cooked Semimembranosus meat samples were measured. Increase in pH, cooking loss, collagen solubility and tenderness scores with decrease in shear force value and collagen content was observed with increases in cooking temperature and time. However, no statistical difference was observed for shear force values, collagen solubility values and tenderness scores in pressure cooked meat and meat cooked in a water bath at 100°C for 45min, inferring that cooking of buffalo meat at 100°C for 45min improved collagen solubility and tenderness to the same extent as that due to pressure cooking.     

Effect of temperature and humidity on the biology of Attagenus fasciatus (Thunberg) (Coleoptera: Dermestidae)

The effect of temperature and relative humidity (r.h.) on the biology of the carpet beetle Attagenus fasciatus was studied under laboratory conditions. The influence of two temperatures (30 °C and 35 °C) and three humidities (40, 60 and 80% r.h.) on the number, duration, mortality and pupation of larval instars, as well as on the biology of fed and starved adult beetles, was investigated. Attagenus fasciatus larvae were reared on dried milk. The mean duration of each successive larval instar generally increased slightly but there was much fluctuation, particularly for the later instars. The highest mortality was recorded during the first two or three instars. At 30 °C pupal duration decreased with increasing r.h. while at 35 °C there was a slight increase. However, the duration at 35 °C was always shorter than at 30 °C. There was 100% emergence of adults from pupae under all test conditions except 40 and 60% r.h. at 35 °C where it fell to about 90%. Humidity and starvation strongly affected egg hatchability under all conditions tested. At 35 °C, eggs took less time to hatch than at 30 °C and there was a positive correlation between egg duration and r.h. The duration of the egg stage was longer for eggs of starved females than those of fed ones. Adult longevity was longer at higher humidity, females lived longer than males and unmated beetles lived longer than mated ones. Starvation reduced adult longevity in all cases. The sex ratio was male biased at 30 °C except at 80% r.h. but the reverse was true at 35 °C.