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.     

CHEMICAL, NUTRITIVE AND SENSORY CHARACTERISTICS OF TOMATOES BEFORE AND AFTER CONVENTIONAL AND MICROWAVE BLANCHING AND DURING FROZEN STORAGE

The objective of this study was to evaluate the effects of microwave blanching on chemical, physical and sensory characteristics of tomatoes prior to and after frozen storage. Tomatoes were blanched (4 min) using four treatments: conventional boiling water (BW), steam (ST), microwaved in a glass container (MW), and microwaved in boilable bags (MWB). The lowest moisture content occurred in MW‐blanched tomatoes before (92%) and after (86%) frozen storage. These tomatoes had the highest reduced ascorbic acid (RAA) content and the highest RAA retention (> 23 mg/100 g, >91%) after blanching and after frozen storage. After blanching, MWB‐blanched tomatoes were the lightest, while after frozen storage, ST‐blanched tomatoes were the lightest. BW‐blanched tomatoes had generally higher flavor, texture and appearance scores. This study demonstrated that though visual color and sensory attributes were highest for BW‐blanched tomatoes, MW‐blanched tomatoes retained more nutritive value in the finished product.     

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.     

Polyphenol oxidase activity and implications on the quality of intermediate moisture and dried apples

This study aimed at investigating the water activity threshold for the polyphenol oxidase activity in Golden Delicious apple. Freeze-dried powders obtained from blanched and unblanched apples were equilibrated and stored at four water activity levels, ranging from 0.11 to 0.56, at 20 and 40 °C, to differentiate between nonenzymatic and enzymatic browning. The contents of hydroxycinnamic acids, phloridzin, catechin, epicatechin, polymeric flavan 3-ols, and 5-hydroxymethylfurfural, the antioxidant activity values, and the Hunter colorimetric parameters of apple products were analyzed. Results showed that no polyphenol oxidase activity occurred in unblanched dehydrated apples stored at water activity levels between 0.11 and 0.32. In this water activity range, blanching pre-treatment accelerated the Maillard reaction in the products stored at 40 °C, as observed from both higher 5-hydroxymethylfurfural formation and more intense red color development in blanched apples with respect to the unblanched ones. At the water activity level of 0.56, both increased redness and higher antioxidant degradation were observed in the unblanched apples with respect to the blanched apples, indicating that the threshold water activity for polyphenol oxidase was in the range 0.32–0.56. Among apple antioxidants, epicatechin was mostly affected by polyphenol oxidase activity, either by direct oxidation or by a coupled oxidation mechanism. Therefore, “mild” pre-heating treatments or no pre-treatments could be proposed when the apple is to be stored and used at water activity ≤0.32, whereas blanching should be applied for intermediate moisture apples or in food applications where moisture transfer from other ingredients could bring apples above this critical water activity level.     

Preparation, Evaluation and Analysis of a French-Fry-Type Product from Sweet Potatoes

A French-fry-type product was prepared from ‘Jewel’ and ‘Centennial’ sweet potatoes. Samples were prepared from freshly harvested, cured, and stored, cured roots. The roots were peeled, sliced into strips and blanched in hot water. The blanched strips were partially dehydrated by one of five treatments and then frozen at ?30°C. Frozen strips were fried in hot peanut oil and evaluated by a sensory panel. Strips prepared by dehydration in a hot air tunnel at 120°C for 5 min were favored by the sensory panel. Blanching removed significant amounts of dry matter and resulted in partial hydrolysis of the starch by endogenous enzymes. Sensory color scores were not affected by reducing sugar content. Sensory flavor scores were related to total sugar content.     

Water Blanching Effects on Headspace Volatiles and Sensory Attributes of Carrots

Carrots blanched in water for 0 to 300 sec were analyzed for flavor volatiles by dynamic headspace analysis, the volatiles identified by gas chromatography/mass spectrometry, and the sensory attributes evaluated by a trained panel to determine quality changes as related to blanching times. Most volatiles, in particular terpenoids (sabinene, β-pinene, β-myrcene, limonene, trans-caryophyllene, α-humulene, β-bisabolene and α-farnesene) decreased by at least 50% within 60 sec of blanching. Ratings on quality attributes of color, texture, raw carrot aroma, sweetness, flavor and overall impression decreased with blanching time, while cooked carrot aroma increased. There were correlations (p < 0.05) between blanching times, flavor volatiles and sensory attributes.     

Changes in total phenolic content and color of bottle gourd (<Emphasis Type="Italic">Lagenaria siceraria</Emphasis>) juice upon conventional and ohmic blanching

Plant phenolics exist in a complex matrix and require a high separation capacity for analysis. Bottle gourd (BG) was blanched using conventional thermal and alternate thermal ohmic heating methods using different combinations of temperature (60–90°C) and time (1–5min), and the effect of these methods on total phenolic content (TPC) and color was examined. Complete characterization on the basis of the phenolic profile of unblanched, ohmically blanched, and conventionally blanched samples of BG was studied. Gas chromatography-mass spectrometry and Liquid chromatography-mass spectrometry were used to detect volatile and nonvolatile phenolic compounds, respectively. The color profiles of the unblanched and conventionally and ohmically blanched samples were studied via hunterLab colorimeter using L*, a*, and b* coordinates. The highest increase in TPC was observed at 80°C, 4 min and 90°C, 5min in the case of ohmic and conventional blanching, respectively. The conventionally and ohmically blanched samples both produced desirable green-color retention in comparison to the unblanched samples; however, highest retention was observed in the ohmically blanched samples. The ohmically blanched samples exhibited the maximum extraction of phenolic compounds and better color of BG juice in comparison to the other samples.     

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.     

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.     

Influence of ohmic heating/osmotic dehydration treatments on polyphenoloxidase inactivation,physical properties and microbial stability of apples (cv. Granny Smith)

The combined effect of ohmic heating (OH) and osmotic dehydration (OD) with vacuum impregnation (VI), on the polyphenoloxidase (PPO) inactivation, physical properties and microbial stability of apples stored at 5 °C or 10 °C was analyzed. The treatments were performed using a 65% (w/w) sucrose solution and with ohmic heating at 13 V/cm at 30 °C, 40 °C or 50 °C for 90 min. Examination of the dehydrated samples showed that the water loss and the solid gain were greater with the OD/OH and VI/OH treatments at 50 °C. PPO was completely inactivated by the OD/OH and VI/OH treatments at 50 °C. There was a correlation between the PPO activity, the color change and the browning index of the treated and stored samples; the values for these parameters were stable when PPO was inactivated. The lowest loss of firmness and color was obtained with the VI/OH treatment at 50 °C. The shelf-life of the apples treated with VI/OH at 50 °C and stored at 5 °C was extended to more than 4 weeks. Therefore, the VI/OH treatment at 50 °C was determined to be the best process for dehydrating apples.Industrial relevanceThe aim of this research was 1 to study the combined effect of ohmic heating (OH) and osmotic dehydration (OD) with vacuum impregnation (VI) on the polyphenoloxidase inactivation and microbial stability of osmotically dehydrated apples stored at either 5 °C or 10 °C. Two technologies, OH and OD were performed at 30, 40 or 50 °C with an electric field intensity of 13 V/cm and conventional heating for 90 min. The results showed a correlation between the PPO activity, the color change and the browning index of the treated and stored samples; the values were stable when PPO was inactivated. PPO was completely inactivated by the OD/OH and VI/OH treatments at 50 °C. The shelf-life of the apples treated was extended to more than 4 weeks. Under the investigated conditions, VI/OH treatment at 50 °C and stored at 5 °C may be considered the better minimal processing that preserves the fresh-like properties.     

Inactivation of apple (Malus domestica Borkh) polyphenol oxidases by radio frequency combined with pulsed electric field treatment

Radio frequency (RF) preprocessing combined with pulsed electric field (PEF) processing was employed to inactivate polyphenol oxidase (PPO) in apple juice. PPO enzyme levels, loss of total phenolic content (TPC), colours and volatile components in the apple juice were subsequently determined and compared with conventional processing methods (60 °C for 10 min and 70 °C for 10 min). Results indicated that, when the apple tissue was preprocessed using RF for 10 min, the residual activity of PPO decreased to 13.57%; when the squeezed juice was processed by PEF, the residual activity decreased to about 5% at 15–35 kV cm^?1 for 400 μs. RF treatment caused no significant loss in TPC. Compared with the conventionally processed samples, the apple juice that was RF‐treated for 10 min and PEF‐treated at 15 kV cm^?1 for 400 μs increased its lightness and maintained its fresh‐like flavour.     

银杏叶提取液复合涂膜对鲜切苹果品质的影响

以‘红富士’苹果为试材,采用0.5 mg/mL银杏叶提取液及其与1%海藻酸钠复合涂膜两种方式处理鲜切苹果,从色泽、硬度、质量损失率、VC含量、多酚氧化酶活性、菌落总数以及感官评定等方面对鲜切苹果的保鲜效果进行评价,探讨银杏叶提取液及其复合涂膜对鲜切‘红富士’苹果保鲜的影响。结果表明：银杏叶提取液处理和银杏叶提取液复合海藻酸钠涂膜处理均可降低鲜切‘红富士’苹果贮藏期间的呼吸强度及乙烯释放速率,延缓鲜切苹果可溶性固形物、可滴定酸和VC含量的下降,减缓鲜切苹果的质量损失及硬度的下降,抑制贮藏期间苹果表面微生物的生长,使多酚氧化酶和过氧化物酶的活性维持在较低的水平,较好地维持了鲜切苹果的感官品质,银杏叶提取液复合海藻酸钠涂膜保鲜效果最佳。     

蓝莓混汁加工中的防酶促褐变工艺

蓝莓含有大量的多酚氧化酶（PPO）,在果汁加工过程中易与酚类物质发生酶促褐变反应,影响果汁品质.榨汁前对蓝莓进行防褐变处理可以明显改善蓝莓混汁的品质,本文主要讨论了添加酶抑制剂和蒸汽热烫直接灭酶两种方法及其对果汁品质的影响.榨汁前添加0.05%VC可以抑制PPO与酚类物质反应,但不能使酶完全失活,且不能促进花色苷和多酚类物质的溶出;热烫2 min能使蓝莓的内源性PPO完全失活,防止酶促褐变,并且明显提高了果汁中的花色苷和总酚含量,提高果汁的色泽稳定性.     

Enzyme Inactivation in Food Processing using High Pressure Carbon Dioxide Technology

High pressure carbon dioxide (HPCD) is an effective non-thermal processing technique for inactivating deleterious enzymes in liquid and solid food systems. This processing method avoids high temperatures and exerts a minimal impact on the nutritional and sensory properties of foods, but extends shelf life by inhibiting or killing microorganisms and enzymes. Indigenous enzymes in food such as polyphenol oxidase (PPO), pectin methylesterase (PME), and lypoxygenase (LOX) may cause undesirable chemical changes in food attributes, showing the loss in color, texture, and flavor. For more than two decades, HPCD has proved its effectiveness in inactivating these enzymes. The HPCD-induced inactivation of some microbial enzymes responsible for microbial metabolism is also included. This review presents a survey of the published knowledge regarding the use of HPCD for the inactivation of these enzymes, and analyzes the factors controlling the efficiency of HPCD and speculates on the underlying mechanism that leads to enzyme inactivation.     

Effects of Low-dose Gamma Irradiation and Conventional Treatments on Shelf Life and Quality Characteristics of Diced Celery

ABSTRACT: The effects of 0.5 and 1.0 kGy gamma irradiation on microbial and sensory characteristics of diced celery were compared to conventional treatments such as acidification, blanching, and chlorination. Aerobic plate counts for the irradiated celery did not exceed 10⁷ CFU/g, in contrast, the acidified, blanched, chlorinated, and control samples surpassed aerobic microbial counts of 10⁸ CFU/g in 22, 19, 12, and 8 d, respectively. Importantly, the 1.0-kGy treatment eliminated inoculated Listeria monocytogenes and E. coli. While the acidified and blanched samples had significantly different sensory profiles compared to the other treatments, the irradiated samples maintained their color, texture, and aroma longer and were preferred in the sensory tests. The sensory shelf life of the 1.0-kGy-treated celery was 29 d compared to 22 d for the control, chlorinated, and 0.5 kGy, and 15 d for the acidified and blanched celery.     

Physicochemical and Sensory Evaluation of 'Rocha' Pear Following Controlled Atmosphere Storage

ABSTRACT: The effects of several processing factors (storage time, time in the open air at room temperature, and overhead concentrations of O₂ and CO₂) on color, firmness, polyphenol oxidase (PPO) activity, and sensory attributes of pears (cv. Rocha) grown in 2 locations were studied using a multiple linear regression model. Backward elimination (F ≥ 0.005) was used to assess the significant factors. Extended storage time, long‐time exposure at room temperature, and high O₂ concentration played major roles on color changes assessed instrumentally and further confirmed by a sensory panel. Firmness was strongly affected by storage time and by time in the open air at room temperature. Finally, PPO activity was dependent on the growing location.     

Effects of low temperature blanching on texture,microstructure and rehydration capacity of carrots

The effect on quality of stepwise blanching (first 10 min at 65 °C, 50 min holding time, and 1 min at 95 °C) prior to drying of carrot slices was compared with conventional blanching (95 °C, 1 min). As quality parameters, rehydration capacity (effective diffusivity D_e, equilibrium moisture content W_e), texture (puncture test) and microstructure (SEM and Cryo‐SEM) were chosen. Non‐significant differences were found between the W_e of stepwise blanched samples and conventionally blanched ones, both values being similar to the moisture content of fresh carrots. D_e of conventional blanched carrots was higher than for stepwise blanched ones. Maximum force of stepwise blanched samples was higher than those of conventionally blanched ones and not significantly different from fresh carrots. Microstructural observations showed that stepwise blanching preserved cell to cell contacts better than conventional blanching; this fact was attributed to pectin‐methyl‐esterase activation at 65 °C, resulting in the differences in the maximum force between both treatments. Conventionally blanched samples tended to separate along their cell walls, forming voids among the phloem parenchyma cells. These voids would be filled with water during rehydration, thus showing the slightly higher W_e and the higher D_e for conventionally blanched carrots. Copyright © 2005 Society of Chemical Industry     

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.