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.     

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.     

The effect of preliminary processing and period of storage on the quality of frozen Boletus edulis (Bull: Fr.) mushrooms

This paper investigates the effect on the quality of frozen Boletus edulis (Bull: Fr.) mushrooms of blanching or soaking and blanching in aqueous solutions containing combinations of added substances safe for human consumption, or period of frozen storage. During 12 months of storage, sensory evaluations, instrumental colour measurements and chemical analyses of the frozen products were carried out every four months. Based on the results of the sensory evaluation, a maximum storage period of four months was set for the frozen product obtained from unblanched mushrooms. Frozen products having undergone preliminary processing retained good sensory quality for up to 12 months. Soaking, blanching and freezing resulted in the appearance of colours, such as yellow, honey and pink–violet. As a result of freezing, decreases in the contents of thiamine, riboflavin and vitamin C were noted. Blanching in water, as a method of pre-processing, was sufficient for maintaining acceptable sensory quality.     

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.     

Study of lipoxygenase and peroxidase as blanching indicator enzymes in peas: change of enzyme activity,ascorbic acid and chlorophylls during frozen storage

In this study, the effects of different blanching conditions on residual lipoxygenase (LOX) and peroxidase (POD) activities and quality changes in peas during frozen storage were studied. Peas were analysed for LOX and POD activities, ascorbic acid and chlorophylls a and b contents at 1, 2, 3, 6, 9 and 12 months of frozen storage. No regeneration of LOX and POD activities was determined in frozen-stored peas at −18 °C. The degradations of ascorbic acid and chlorophylls followed first-order kinetics. The half-lives of ascorbic acid, chlorophylls a and b derivatives in unblanched peas were found to be 3.30, 14.01 and 36.76 months during storage, respectively. Blanching at both 70 °C for 4.0 min and 80 °C for 2.0 min increased the half-life of ascorbic acid while it decreased those of chlorophylls a and b. Overall results suggested a blanching time of 2.0 min at 80 °C to inactivate 90% of initial POD activity, so, to retain quality parameters such as ascorbic acid and chlorophyll pigments in a storage period of 12 months at −18 °C.     

Effect of enzyme activity and frozen storage on jalapeño pepper volatiles by selected ion flow tube-mass spectrometry

Abstract: Samples of unblanched (fresh), stannous chloride-treated, or blanched jalapeño peppers were measured for real-time generation of lipoxygenase-derived volatiles during 10 min after tissue disruption. Volatiles were also measured before and after 1.5, 2.5, 3, 6, and 9 mo of frozen storage at −15 °C. The concentration of all lipoxygenase-derived compounds was significantly higher in unblanched jalapeño peppers compared to enzyme inhibited peppers. The maximum concentration of (Z)-3-hexenal, (E)-2-hexenal, and hexanal was detected at about 1.2, 1.5, and 1.5 min after tissue disruption, respectively. A decrease in (Z)-3-hexenal and an increase in dimethyl sulfide and methylbutanal occurred in blanched compared to stannous chloride-treated peppers due to heat. Frozen storage resulted in no major changes in the lipoxygenase-derived volatiles of whole and pureed blanched peppers after 9 mo. However, in whole unblanched peppers a gradual decrease of (Z)-3-hexenal, (E)-2-hexenal, hexanal, hexenol, and hexanol was observed over time; whereas in pureed unblanched peppers these compounds increased, reached maximum concentration, and then decreased. Similarly, the minor volatiles 2-pentenal, 1-penten-3-one, (E)-2-heptenal, (E)-2-octenal, and (E)-2-nonenal showed an initial increase followed by a decline in both whole and pureed unblanched peppers. Tissue disruption increased generation and degradation rates during frozen storage. The compounds (E,Z)-2,6-nonadienal, n-propyl aldehyde, 2-isobutyl-3-methoxypyrazine, and a mixture of terpenes decreased in unblanched and blanched frozen samples, while nonanal and methylbutanal increased only in unblanched samples. Practical Application: Data obtained in this study contribute to the understanding of the dynamics of lipoxygenase-derived volatile formation upon tissue disruption of jalapeño pepper. In addition, it contributes to generate knowledge on the effect of processing techniques, namely blanching and frozen storage, on the volatile profile of these peppers. This knowledge has applications in the manufacturing, product development, and quality control areas of the food industry as useful information to help in the designing and monitoring of processes aimed to obtain products with specific aroma characteristics. For instance, maximum levels of “fresh” and “green” aroma compounds are achieved rapidly during the first few minutes after pepper tissue is disrupted. The inhibition of enzyme activity shortly after this may help to maximize concentration of these aroma notes in the product. Frozen storage produces enzymatic and chemical changes in the volatile profile of unblanched peppers. The aroma profile of blanched peppers is more stable under frozen conditions, with a lower total volatile concentration.     

Impact of frozen storage on polyacetylene content, texture and colour in carrots disks

This study investigated the effect of freezing method (slow or blast freezing) with or without blanching during storage at −20 °C on the levels of three polyacetylenes, falcarinol (FaOH), falcarindiol (FaDOH), falcarindiol-3-acetate (FaDOAc) in carrot disks. The quality of the carrot disks was also assessed using instrumental texture and colour measurements. Blast frozen carrot disks retained higher amounts of polyacetylenes compared to their slow frozen counterparts. Whilst the levels of retention of total polyacetylenes was higher in unblanched than blanched disks prior to freezing there was a sharp decrease in the levels of polyacetylenes in unblanched frozen carrots during the storage period for 60 days at −20 °C. FaDOH was observed to be the most susceptible to degradation during frozen storage of unblanched carrot disks, followed by FaOH and FaDOAc. The changes in the level of polyacetylenes during storage were adequately described by using Weibull model. The texture and colour were also found to decrease during frozen storage compared to fresh carrots.     

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 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.     

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.     

EFFECT OF BLANCHING ON STORAGE STABILITY OF HAZELNUT MEAL

Influence of blanching on storage stability of hazelnut meal was investigated under accelerated storage conditions. Meals were obtained from unblanched and blanched hazelnut kernels, and stored at a relative humidity of 60% at 30C for 50 days. Total free fatty acid content, concentrations of individual free fatty acids, peroxide value and oil stability index were measured in the hazelnut meal samples during storage. No significant difference was found between peroxide values of the samples, however, the values of both samples increased during storage time. The concentrations of free fatty acids increased because of the activity of lipase in both meals, but the levels were lower in the blanched sample. Oil stability index of the unblanched sample was lower than that of the blanched sample. Blanching treatment was found to improve the oxidative stability of hazelnut meal, possibly because of partial inactivation of deteriorative enzymes.

PRACTICAL APPLICATIONS

Hazelnut meal is a product obtained from hazelnut which is used as an ingredient in various food products. Hazelnut meal is more prone to degradation and quality loss during storage via oxidation compared with the whole counterpart. Stability of whole hazelnut has been studied to a great extent in the literature, but there is a scarcity of information regarding stability of processed hazelnut. In addition, there is no information in the literature about the amount of individual free fatty acids in hazelnut where the amounts of total free fatty acids have been reported extensively. This study provides data for quality and stability of hazelnut meal during storage which could be used by the food industry.     

Influence of blanching and low temperature preservation strategies on antioxidant activity and phytochemical content of carrots, green beans and broccoli

The objective of this study was to investigate the effect of blast freezing and blanching in combination followed by chilling, on the antioxidant activity (ARP), phenols, ascorbic acid and colour of broccoli, carrots and green beans. No significant changes (p > 0.05) in ARP of blanched frozen (BLFR) broccoli, carrot and green beans were observed. In contrast, UBFR (unblanched frozen) treatments caused a significant decrease (p < 0.05) in ARP and ascorbic acid content of vegetable samples. BLFR treated samples had better retention of antioxidant activity and ascorbic acid as compared to UBLR counterparts at chill storage (4 °C) for 7 days. However, no significant changes were observed in phenol content for all vegetables. Ascorbic acid decreased exponentially for both blanched and unblanched samples. The reaction rate constant (k) increased from 1.06 × 10⁻¹ day⁻¹ to 1.17 × 10⁻¹ day⁻¹ for blanched and unblanched broccoli florets and from 4.6 × 10⁻³ day⁻¹ to 1.98 × 10⁻¹ day⁻¹ for blanched and unblanched carrots during 7 days storage. Result presented here indicates greater stability of nutritional parameters for BLFR samples compared to UBFR samples during 7 days storage at 4 °C for all vegetables.     

漂烫对速冻苹果丁过氧化物酶活性及品质的影响

为了优化速冻苹果丁漂烫工艺,以新鲜富士苹果(切分为1.5 cm×1.5 cm×1.5 cm的小丁)为研究对象,采用响应曲面法,建立漂烫时间、漂烫温度、料液比对POD相对酶活影响的二次多元回归数学模型,并分析漂烫对其品质的影响。结果表明:抑制速冻苹果丁POD酶活性的最佳漂烫条件为:漂烫时间4.5 min、漂烫温度92℃、料液比1∶11(g/m L);未漂烫速冻苹果丁的ΔE值升高了36.10,感官品质降低了34.46,可溶性固形物、可滴定酸及VC损失率分别为28.25%、17.67%、20.13%,漂烫后速冻苹果丁的ΔE值升高了5.57,感官品质降低了7.27,可溶性固形物、可滴定酸及V_C损失率分别为24.42%、10.85%、12.16%。表明漂烫处理较好地保持速冻苹果丁的品质。      

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.     

A simple blanch-dry process for lipoxygenase inactivation in soybean cotyledons

Full-fat flour from unblanched soybeans develops a beany flavour during milling due to lipoxygenase activity; the flour also becomes bitter during storage. The minimum thermal treatment necessary to inactivate lipoxygenase in soybeans before milling was determined. Soybeans were dehulled and cotyledons blanched in water between 80 and 99.3°C. Water blanching for 3 min at 99.3°C was necessary when blanched cotyledons were subsequently sun dried, and the flour had a nitrogen solubility index (NSI) of 37.8% and residual trypsin inhibitor activity (TIA) of 64.2%. Only 1.5 min blanching was necessary to inactivate lipoxygenase in soy cotyledons if they were dried subsequently at 60°C; NSI of this flour was 32.7%, with 44.7% residual TIA.     

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.     

Peroxidase and Lipoxygenase Influence on Stability of Polyunsaturated Fatty Acids in Sweet Corn (Zea mays L.) during Frozen Storage

The effect of blanching treatments and packaging materials on lipoxygenase (LOX) and peroxidase (POD) activity and fatty acid stability of two cultivars of sweet corn (Jubilee and GH-2684) were evaluated during 9 mo storage at ?20°C. Complete inactivation of LOX and POD was obtained with 9 and 15 min of steam blanching, respectively. Relative fatty acid content revealed no change in fatty acid composition during storage. Control of degradation of polyunsaturated fatty acids (PUFA) did not depend on oxygen permeability of different packaging materials. Blanching had little effect on PUFA degradation after 9 mo storage.     

Effects of blanching and sulphur dioxide on ascorbic acid and pigments of frozen capsicums

The frozen storage of capsicum tissue for 1 year at −12°C resulted in appreciable losses (from 10 to 58%) of ascorbic acid dependent upon the cultivar and the extent of tissue blanching. Ascorbic acid retention was maximal, but retention of chlorophyll a was minimal and pH dependent, in frozen blanched tissue which accordingly showed a greater increase in pheophytin formation. Sulphite treatment of unblanched tissue maintained acceptable colour through retardation of degradative interconversion and isomerization reactions of chlorophyll and carotenoid pigments during frozen storage.     

氯化钙处理对速冻蓝莓冻藏期品质的影响

研究不同质量分数氯化钙处理对速冻蓝莓果实于－18 ℃冻藏时品质变化的影响。结果表明：随着冻藏时间延长,速冻蓝莓果实的质量、硬度、可溶性固形物（TSS）、可滴定酸、VC、花色苷和总酚含量均呈下降趋势。浸钙处理可延缓速冻蓝莓果实质量、硬度、TSS、可滴定酸、VC、花色苷和总酚含量的下降,保持果实原有品质。在整个冻藏期多酚氧化酶（PPO）和过氧化物酶（POD）活性不断下降,氯化钙处理组冻藏后期PPO活性明显被抑制,但对POD活性没有显著效果。综合分析各指标,经1.5%氯化钙溶液处理的速冻蓝莓其冻藏期品质最好。     

Steam blanching effect on polyphenoloxidase,peroxidase and colour of mango (Mangifera indica L.) slices

The heat stability of peroxidase (POD) and polyphenoloxidase (PPO) was investigated in mango (Mangifera indica L.) slices, and the relative colour was studied after different steam blanching times. There was complete inactivation after 5 min for POD and 7 min for PPO. Steam blanching of 3 min gave residual activity of 2.85% and 8.33% for PPO and POD, respectively, and when compared with samples blanched for 5 min had no effect on colour over 20 days of storage. Correlation was found between activities of PPO, POD and colour change over 20 days. After 7 min steam blanching the browning index was stable but less than at 3 and 5 min because non-enzymic browning had occurred. This research suggests that yellowness (b) and lightness (L) values contribute positively to the browning index (BI), compared to redness (a).