PHYSICAL, CHEMICAL AND SENSORY QUALITY OF MICROWAVE-BLANCHED SNOW PEAS

Snow peas were blanched using four methods [conventional boiling water (BW); steam (ST); microwave (MW); and microwave blanched in heat sealable bags (MWB)], then held frozen at (～18C) for four weeks. Immediately after blanching, MWB‐blanched snow peas retained more reduced ascorbic acid (RAA; 72%), than other treatments. Blanching treatment had no effect on lightness [L* value). With the exception of BW‐blanched peas, blanching significantly altered color. After frozen storage, MWB‐ and MW‐blanched samples both contained about 26 mg/100 g RAA, significantly more RAA than other treatments. MWB‐blanched peas generally had as high or higher sensory appearance, aroma, flavor, texture and general acceptability scores than other treatments. These results imply that blanching snow peas in a heat‐sealable microwave bag, prior to frozen storage, produces a product of equivalent sensory quality and superior nutritional quality compared with more conventional blanching methods.     

MICROWAVE BLANCHING EFFECTS ON COLOR, CHEMICAL AND SENSORY CHARACTERISTICS OF FROZEN ASPARAGUS

Asparagus was blanched for 4 min using: conventional boiling water (BW), steam (ST), microwave (MW), or microwave heated in boilable bags (MWB). Samples were ice-cooled, bagged, heat-sealed and stored at ?18C for 4 weeks. Peroxidase activity was reduced from 98–114 units in fresh, unblanched to 1–7 units in blanched asparagus. Reduced ascorbic acid (RAA) content in fresh, unblanched asparagus was ～49 mg/100 g; RAA content in fresh, BW-blanched asparagus was ～44 mg/100 g. Frozen, unblanched asparagus retained about 40% of original RAA content; BW-blanched asparagus retained 61%, and MWB-blanched asparagus retained 87%. After frozen storage all samples were darker than freshly blanched samples. Blanching increased and freezing decreased greenness of all samples. Blanching increased yellowness of fresh samples; after frozen storage, blanching treatment differences were lost. Unblanched samples had the highest appearance scores; unblanched and MW-blanched samples had the highest color scores. Overall quality of the microwave blanched asparagus was as good as or superior to conventionally blanched asparagus.     

MICROWAVE AND CONVENTIONAL BLANCHING EFFECTS ON CHEMICAL, SENSORY, AND COLOR CHARACTERISTICS OF FROZEN BROCCOLI

Broccoli (cv. Empress) obtained from a local supplier was blanched within 15 h of harvest. It was blanched by four methods in covered containers: conventional boiling water (1900 mL, 4 min) (BW), steam (300 mL water, 4 min) (ST), microwave heated in 1 L glass containers (60 ml water, 4 min, 700 W) (MW), and microwave heated in 1 L Seal-a-Meal^TM bags (45 ml water, 4 min) (MWB). Aliquots were frozen at -18C for 4 weeks. Fresh unblanched broccoli peroxidase activity ranged from 389 to 829 units/min; activity was essentially zero immediately after all blanching treatments. The highest reduced ascorbic acid (RAA) content occurred in fresh unblanched broccoli. Some peroxidase regeneration occurred during frozen storage. Immediately after blanching, all blanched broccoli had lower RAA content than control broccoli. MW-blanched broccoli retained the greatest amount of RAA and had appearance, visual color, texture scores, and chroma of florets and stems equivalent to ST-blanched broccoli. MW-blanched broccoli had flavor and general acceptability scores similar to BW-blanched broccoli. After 4 weeks in frozen storage, MW-blanched broccoli had the highest RAA content.     

MICROWAVE BLANCHING EFFECTS ON CHEMICAL, SENSORY AND COLOR CHARACTERISTICS OF FROZEN GREEN BEANS

Green beans (cv. Mustang) obtained from the University of Illinois at Urbana-Campaign Horticulture plots were assayed within 3 h of harvest. Beans were blanched in covered containers: conventional boiling water (1900 ml, 3 min) (BW), steam (300 ml water, 3 min) (ST), microwave heated in 1 L glass containers (60 ml water, 3 or 5 min, 700 W) (MW-3, MW-5), and microwave heated in 1 L Seal-a-Meal^TM bags (45 ml water, 3 min) (MW-Bag). Baseline data were collected immediately after blanching. Aliquots were frozen at – 18C for 4 weeks. Unblanched beans had 82 units of peroxidase activity/min; activity was zero immediately after all blanching treatments. Reduced ascorbic acid (RAA) content was highest for unblanched, ST and MW-5 beans and lowest for BW and MW-Bag beans immediately after blanching. ST beans retained 100% of original RAA. Instron shear force (kg) was highest for unblanched beans and lowest for BW and MW-Bag beans immediately after blanching. After frozen storage, ST and BW beans had the lowest shear values. Visual color was poorest for MW-5; other treatments were not different. Microwave blanching green beans for 3 min in a covered container or bag prior to 4 weeks frozen storage resulted in a product that was not different in RAA content, retention or color from BW blanched beans; however, these samples differed in tenderness and crispness from boiling water blanched beans.     

ENZYME ACTIVITY AND QUALITY OF FROZEN GREEN BEANS AS AFFECTED BY BLANCHING AND STORAGE

Effects of different blanching conditions on residual enzyme activities and quality changes in green beans during frozen storage were studied. Green beans were blanched at various temperature and time combinations at both pilot plant and commercial scales. After storage at —23°C for 3, 6, 9 and 12 months they were analyzed for residual activities of catalase, lipoxygenase, polyphenoloxidase and peroxidase; changes in sensory quality as evaluated by a taste panel; and color and firmness as measured with instruments. Most of enzymes were inactivated during normal blanching but the residual activities varied among enzymes. Beans blanched above 82°C for 3.5 min yielded higher sensory scores for the quality attributes tested than those blanched at the lower temperatures. However, there appears to be no direct relationship between the quality attributes measured and the residual enzyme activities during 12 months storage.     

EFFECTS OF CULTIVARS, BLANCHING TECHNIQUES, AND COOKING METHODS ON QUALITY OF FROZEN GREEN BEANS AS MEASURED BY PHYSICAL AND SENSORY ATTRIBUTES

Effects of cultivars, blanching techniques, and cooking methods on the color, texture, and sensory characteristics of frozen green beans were investigated. Provider beans were firmer than the Contender cultivar following frozen storage and cooking when evaluated instrumentally and by a sensory panel. Microwave-blanched beans were harder according to Instron measurements, and sensory scores for firmness and toughness were higher than beans blanched by boiling water or steam. Green beans blanched or cooked by microwaves had grassy aromas and strong off-flavors that were not detected in those blanched or cooked by conventional methods. Microwave cooked beans were greener and firmer than those conventionally cooked.     

Lipoxygenase as Blanching Index for Frozen Vegetable Soybeans

Blanched samples of frozen vegetable soybeans using peroxidase (POD) and lipoxygenase (LIP) as blanching indices were compared with unblanched samples during storage by sensory evaluation, vitamin C determination and remaining enzyme activity. Samples using LIP and POD as blanching indices showed no significant differences in sensory quality during 160-day frozen storage, while both treatments were significantly different from unblanched samples. Vitamin C in samples using LIP as blanching index was higher than that in unblanched ones but not significantly different from that in samples using POD as an index. Samples using LIP as blanching index had 11.5% POD activity but no LIP activity, while blanched samples using POD as blanching index had no LIP or POD activities during storage.     

EFFECT OF BLANCHING AND SULFITE TREATMENT ON THE QUALITY OF FROZEN CAULIFLOWER

The influence of blanching time and post-blanching sulfite treatment on the sensory quality and texture of frozen cauliflower were assessed after storage at -18°C for up to one year. The treated cauliflower florets, sealed in polyethylene bags, were placed in waxed paperboard cartons and frozen in a contact plate freezer at -35°C. Samples blanched for 3 min and dipped in a solution containing 1000ppm of SO₂ for 5 min gave a significantly (p<0.05) superior product even when stored for one year. The residual SO₂ content of 50 ppm found in these stored samples disappeared after a 3 min cooking in boiling water. Cauliflower texture was influenced by blanching time but the textural differences of blanched samples diminished following freezing and storage. After a 3 min cooking, the texture of all thawed samples were comparable to that of fresh cauliflower cooked for 10–12 min.     

EFFECTS OF BLANCHING METHOD ON THE QUALITY CHARACTERISTICS OF FROZEN PEAS

This study evaluated the effects of microwave blanching prior to freezing as an alternative pretreatment for frozen peas. Peas were blanched (steam‐, boiling water immersion‐, microwave‐ or microwave‐blanched in a bag), frozen and evaluated after 0, 6 and 12 weeks for moisture and ascorbic acid content, peroxidase activity, visual appearance and instrumental color, and after 6 and 12 weeks for aroma, flavor and texture. All blanch treatments reduced peroxidase activity by 97% compared with controls (unblanched); blanching methods did not differ. Steam blanching resulted in significantly better ascorbic acid retention than all other treatments; microwave blanch treatments were either equivalent to or better than boiling water immersion. Both microwave treatments darkened (L* value) peas. Microwave‐blanched peas were visually greener than other treatments, but their appearance was less intact. Aroma and flavor were similar among blanch treatments. Texture of boiling water immersed peas was similar to the two microwave treatments.     

Evaluation of the amino acid content and sensory value of flageolet bean seeds (Phaseolus vulgaris L.) as affected by preprocessing methods before freezing

The aim of the work was to evaluate the content of amino acids in flageolet bean seeds, prepared for consumption from frozen products obtained using different methods. One of the frozen products was obtained using the traditional method (blanching–freezing–frozen storage) and then cooked. The other was obtained using the modified technology (cooking–freezing–frozen storage), followed by defrosting and heating in a microwave oven. The culinary and technological processing applied brought about a pronounced decrease in tyrosine content (35–47% in 16 g N). The content of the remaining amino acids decreased or increased in relation to the raw material within the extremes of ?15% to +17%. Sulphur amino acid was the limiting amino acid. Product obtained using traditional method had the higher quality protein (EAA index 144–166) of seeds prepared for consumption. In sensory test products, blanched before freezing were evaluated a bit higher than those cooked before freezing (ready‐to‐eat).     

Changes in the radical-scavenging activity of bitter gourd (Momordica charantia L.) during freezing and frozen storage with or without blanching

The effects of blanching, freezing, and frozen storage on the retention of radical-scavenging activity (RSA), total phenolics, and ascorbic acid in bitter gourd were investigated. Blanching of sliced bitter gourd resulted in considerable losses of RSA and total phenolics, and most extensively, of ascorbic acid. In the subsequent frozen storage at -18 degrees C, RSA and total phenolic content of unblanched and blanched bitter gourd underwent little change for 90 d then gradually declined, but at -40 degrees C, they practically remained unchanged throughout the entire storage period. On the contrary, ascorbic acid content of both unblanched and blanched bitter gourd decreased abruptly at the early stage in frozen storage. The results show that blanching of bitter gourd improves the retention of RSA and total phenolics during subsequent frozen storage but markedly aggravated loss of ascorbic acid. Finally, it is to be noted that RSA, total phenolics, and ascorbic acid originally contained in the raw bitter gourd were overall best retained by quick freezing followed by frozen storage at -40 degrees C without preceding blanching.     

热烫前处理对鲜食玉米贮藏过程中保鲜品质的影响

由于鲜食玉米在贮藏期间品质会不断下降,本文利用热烫对鲜食玉米进行前处理,研究其对贮藏期间品质的影响。对鲜食玉米先进行热烫,然后用复合生物保鲜剂进行保鲜,分析含水量、质量损失率、TPA指标、气味与感官品质等,研究贮藏期间鲜食玉米的品质变化。结果表明,热烫前处理的鲜食玉米在贮藏期间,水分含量显著(p<0.05)高于对照,热烫处理可有效抑制鲜食玉米水分散失。热烫处理的鲜食玉米在贮藏0~10 d时,质量损失率略低于对照,30 d时高于对照2.2%,但差异不显著(p>0.05)。热烫处理鲜食玉米的弹性、粘性及回复性与对照差异不显著;而内聚性显著高于对照(p<0.05),硬度、胶粘性和咀嚼性均极显著高于对照(p<0.01)。热烫处理的鲜食玉米气味变化较小。热烫处理对鲜食玉米的保鲜效果较好,能较好保持色、香、味等感官品质。     

Compositional and chill storage characteristics of microwave‐blanched sutchi catfish (Pangasianodon hypophthalmus) fillets

The effect of microwave blanching on quality characteristics of vacuum and conventional polyethylene‐packed sutchi catfish fillets was evaluated under chilled condition. Emphasis has been given to retain the sensory characteristics such as colour and textural properties, which is a major problem in sutchi catfish fillets during extended chill storage. In general, microwave blanching imposed minimum changes on fatty acid and mineral composition of fish meat. A marginal increase in fat content was recorded after microwave heating of fish fillets. The microwave‐blanched fillets showed minimum cooking loss of 3.2 mL per 100 g meat. A slower increase in spoilage parameters was obtained with microwave‐blanched samples compared with unblanched samples, demonstrating the higher storage stability of the sample under chilled conditions. Microwave heating of fish fillets coupled with quick‐chilling and packing under vacuum improved the colour and texture stability of sutchi catfish fillets to a considerable extent. Microwave blanching increased the hardness and chewiness values and decreased the stiffness values of fish fillets. The biochemical and sensory evaluation of microwave‐blanched and vacuum‐packed sutchi catfish fillets showed extended storage life of 21 days, compared with 12 days for unblanched vacuum‐packed samples.     

Influence of modified blanching treatments on inactivation of Salmonella during drying and storage of carrot slices

Documented outbreaks of human illness associated with consumption of minimally processed produce have increased in recent years. This study evaluated the influence of modified treatments on inactivation of Salmonella during preparation, home-type dehydration (60 degrees C, 6h) and storage of carrot slices. Inoculated (five strains, 7.8 log cfu/g) slices were subjected to the following treatments: (i) untreated control, (ii) steam blanching (88 degrees C, 10 min), (iii) water blanching (88 degrees C, 4 min), (iv) blanching in a 0.105% citric acid solution (88 degrees C, 4 min), or (v) blanching in a 0.21% citric acid solution (88 degrees C, 4 min), dried for 6h at 60 degrees C (140 degrees F), and stored for up to 30 d. Bacterial populations were reduced by 3.8-4.1, 4.6-5.1 and 4.2-4.6 log cfu/g immediately following steam, water or citric acid blanching, respectively. After 6h of dehydration, total reductions were 1.6-1.7 (control), 4.0-5.0 (steam blanched), 4.1-4.6 (water blanched) and 4.9-5.4 (blanched in citric acid solution) log cfu/g. Populations continued to decrease throughout storage, but were still detectable by direct plating at 30 d on all samples except for those blanched in 0.21% citric acid. Results suggest that blanching carrot slices, particularly blanching in 0.21% citric acid, before drying should enhance inactivation of Salmonella during home-type dehydration and storage.     

Residual peroxidase activity as influenced by blanching,SO2 treatment and freezing of cauliflowers

The influence of blanching time and SO₂ treatment on the residual peroxidase activity and its implication for the sensory quality of frozen cauliflowers were assessed after storage for up to one year at ?18°C. The treated cauliflowers, sealed in polythene bags, were placed in waxed paperboard cartons and frozen in a contact plate freezer at ?35°C. The sensory quality of frozen stored cauliflowers related well to their residual peroxidase activity, which was sensitive to the SO₂ treatment. Blanched cauliflowers following a brief dip in a metabisulphite solution prior to freezing gave a significantly (P<0.05) superior product even when stored for one year. The residual peroxidase activity, which ranged from 1 to 5.5% in the blanched samples, was below 1 % in the SO ₂-treated samples, and the SO₂ content of50 ppm found in these stored samples disappeared after 3 min cooking in boiling water.     

Qualitative changes in Pleurotus ostreatus (Jacq.: Fr.) Kumm. mushrooms resulting from different methods of preliminary processing and periods of frozen storage

BACKGROUND: The aim of this study was to investigate the effect of different methods of preliminary processing and periods of frozen storage on the quality of Pleurotus ostreatus (Jacq.: Fr.) Kumm. mushrooms. In pre‐processing, mushrooms were blanched or soaked and blanched in water as well as in aqueous solutions of citric acid, L ‐ascorbic acid and/or lactic acid. During 12 months of storage at ?25 °C, sensory evaluations, instrumental colour measurements and chemical analyses of the frozen products were carried out every 4 months. RESULTS: The greatest changes resulting from technological treatment were found in flavour. At the end of the storage period the content of thiamine and riboflavin decreased by 14–65% and 3–13% respectively compared with the raw material. This was accompanied by changes in total acidity and vitamin C content within the ranges ? 56 to + 61% and ? 97 to + 5% respectively. CONCLUSION: Based on the results of the sensory evaluation, a maximum storage period of 4 months was set for the frozen product obtained from unblanched mushrooms. Mushroom products pre‐processed in aqueous solutions with added substances may be stored for 8 months and those blanched in water for 12 months. Copyright © 2009 Society of Chemical Industry     

Effect of Infrared Blanching on Enzyme Activity and Retention of β‐Carotene and Vitamin C in Dried Mango

The objectives of this work were to evaluate infrared (IR) dry blanching in comparison with conventional water blanching prior to hot air drying of mango to inactivate polyphenol oxidase (PPO) and ascorbic acid oxidase (AAO) enzymes, and to study its effect on color change and retention of vitamin C and β‐carotene. Mango cylinders were blanched under similar temperature–time conditions either by IR heating or by immersion in a water bath during 2 min at 90 °C (high‐temperature‐short‐time—HTST) or for 10 min at 65 °C (low‐temperature‐long‐time—LTLT). After blanching mango was hot air dried at 70 °C. PPO was completely inactivated during the blanching treatments, but AAO had a moderate remaining activity after LTLT treatment (～30%) and a low remaining activity after HTST treatment (9% to 15%). A higher retention of vitamin C was observed in mango subjected to IR dry blanching, 88.3 ± 1.0% (HTST) and 69.2 ± 2.9% (LTLT), compared with water blanching, 61.4 ± 5.3% (HTST) and 50.7 ± 9.6% (LTLT). All‐trans‐β‐carotene retention was significantly higher in water blanched dried mango, 93.2 ± 5.2% (LTLT) and 91.4 ± 5.1% (HTST), compared with IR dry blanched, 73.6 ± 3.6% (LTLT) and 76.9 ± 2.9% (HTST). Increased levels of 13‐cis‐β‐carotene isomer were detected only in IR dry blanched mango, and the corresponding dried mango also had a slightly darker color. IR blanching of mango prior to drying can improve the retention of vitamin C, but not the retention of carotenoids, which showed to be more dependent on the temperature than the blanching process. A reduction of drying time was observed in LTLT IR‐blanching mango.     

Infrared and Microwave as a dry blanching tool for Irish potato: Product quality,cell integrity,and artificial neural networks (ANNs) modeling of enzyme inactivation kinetic

This study evaluated the use of Infrared (IR) and microwave (MW) dry blanching technology as an alternative to the conventional hot water (HW) blanching of Irish potato slices. Product quality, cell integrity, and Peroxidase (POD) inactivation kinetics were investigated. Also, the POD inactivation kinetics curve was fitted with both mathematical models and artificial neural networks (ANNs). The result showed that MW blanching technique had the shortest POD inactivation time (5 and 7 mins), when compared with HW blanching (7 and 9 mins) and IR blanching (18 and 21 mins). IR blanched samples had the lowest colour change, slowest moisture loss, and lower microbial activity when compared with HW and MW blanching, although the level of vitamin C retention was similar with MW blanched samples. Furthermore, MW blanching had lower electrolyte leakage and microstructure damage, and better texture, when compared with HW and IR blanching. ANNs (R² = 1.000, RMSE = 1.1597e-14, and SSE = 2.8994e-15) outperformed Weibull distribution (R² = 0.9914, RMSE = 0.0348, and SSE = 0.0073) in fitting the POD inactivation curve. In conclusion, IR and MW technology were efficient in dry blanching of Irish potato, and ANNs allows for smart industrial control and monitoring of dry blanching equipments, since it can combine multiple process variables.     

Effect of blanching,drying, freezing and storage on degradation of β-carotene in different fruits

Since biologically active carotenoids play a significant role in metabolism and because of the fact that its stability can be affected by various factors decomposition degree of β-carotene of various kinds of fruits after drying, freezing, blanching as well as after drying and freezing of blanched fruits has been researched in order to prolong their consumption time-limit. The β-carotene content was determined by means of the spectrophotometric method measuring adsorbance intensity at 450 nm. The results of investigation reveal that the decomposition degree of β-carotene increases significantly with storage time. Depending on the kind of fruits, treatment and storage time it ranged from 6.10% to 68.74%. No significant differences have been found after a longer storage between blanched and non-blanched fruits, either dried or frozen.