Microwave Blanching Research Articles

Effects of various blanching methods on weight loss, enzymes inactivation, phytochemical contents, antioxidant capacity, ultrastructure and drying kinetics of red bell pepper (Capsicum annuum L.)

The effects of hot water blanching (HWB), microwave blanching (MWB), infrared blanching (IRB) and high-humidity hot air impingement blanching (HHAIB) on weight loss, enzyme inactivation (peroxidase, POD and polyphenol oxidase, PPO), characteristic bioactive component contents (red pigments and ascorbic acid), antioxidant capacity (total antioxidant activity and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity), ultrastructure and drying kinetics of red bell peppers under different blanching conditions were investiaged. Results showed that the MWB and IRB treatment yielded lower weight loss than HWB and HHAIB. The inactivation of both PPO and POD enzymes was strongly dependent on blanching temperature and duration and microwave power for microwave blanching. The peppers treated by MWB, IRB, and HHAIB obtained higher red pigments and ascorbic acid retention, total antioxidant activity and DPPH values compared with the samples blanched by HWB. Ultrastructure analysis verified the difference phytochemical contents among four treatments. All four blanching treatments enhanced the drying kinetics relative to unblanched peppers. The Weibull distribution model was employed to calculate the moisture effective diffusivity (Deff), which ranged from 1.2688 × 10−10 to 2.8754 × 10−10 m2/s. The current findings not only contribute to a better understanding of different blanching methods but also provide more data and information for selecting blanching technologies.

Effects of Blanching on Physicochemical Properties of Chantenay Carrots Juice and Assessing the Qualities of Formulated Carrot-MD2 Pineapple Juice Blends

This study was carried out to determine the effects of three blanching methods on carrots and also to assess the physico-chemical and sensory properties of formulated Chantenay carrot-MD2 pineapple juice blend. Hot water, steam and microwave blanching were the methods used and the respective blanching temperatures were 98, 105 and 75 °C for 10 minutes each. Physicochemical properties determined on the juices extracted by gravity from blanched carrots were yield, pH, total soluble sugars, total solids, ash and vitamin C. There were significant differences (p<0.05) in the yield, vitamin C and total solids of the blanched and unblanched carrots. Steam blanching method was chosen for the formulation of the carrot-pineapple juice blend due to its high yield and ash content of 76.65 and 0.66% respectively. The carrot juice from the steam blanching process was formulated with MD2 pineapple juice into various ratios of 50:50, 60:40, 70:30 and 100:0 with the carrot juice being the major component. A preference ranking test carried out on the formulated carrot-pineapple juices indicated that the 50 untrained panellists mostly preferred the 50:50 formulated juice. Proximate and physicochemical analyses were conducted on the 50:50 formulated carrot-pineapple juice and had the following compositions: fat (0.25%), ash (0.25%), protein (0.78%), crude fibre (2.68%), carbohydrates (23.47%), moisture (72.57%), vitamin C (12.40 mg/100 g), β-carotene (955.71 µg/100 g), pH (4.45), total soluble sugars (14.87%) and titratable acidity (1.50%). In conclusion, development of this product will enhance the utilization of carrot not solely for stews and salads but also as a juice blend with the potential to compete with the local and foreign fruit juices on the market. Consumption of the product will help address the resurgence of nutrition-related chronic diseases due to its appreciable content of β-carotene which are potent free radical scavengers in humans.

Microwave Blanching: An Emerging Trend in Food Engineering and its Effects on Capsicum annuum L

AbstractBlanching is the most widely used processing techniques that increases the shelf life of fruits, vegetables and canned food. It softens the fruits and vegetables, aids in peeling and is vital to the canning process. This review elucidates the pros and cons of blanching – both wet and dry – on food products, with a special reference to bell peppers. Agricultural products with high nutritional value and substantial market demand need to be preserved to retain freshness and nutritional qualities till it reaches the processing industry or the consumer. In this review, we described the various attributes of the wet and dry blanching processes with the aim of providing a guide for the reader to design a blanching technique that may maximize the retention of nutrients, micronutrients and volatiles while minimizing the retention of enzymes that cause degradation of fruits and vegetables.Practical ApplicationsThis study shows that microwave blanching of food products is far better approach than other blanching methods as it causes minimal/lesser damage unlike IR blanching and wet blanching methods. This can be said based on the fact that microwave blanching does not involve water as required in the process of wet blanching and, thus, reduces the chances of microbial contamination. The results found in this study can be applied in the development of an optimized blanching approach as to minimize the retention of enzymes that causes degradation and to maximize the retention of nutrients, micronutrients and volatiles.

Influence of different blanching methods on colour, ascorbic acid and phenolics content of broccoli.

Lack of nutrients in cooking water, high energetic costs, high water consumption and recycling are some drawbacks of vegetable blanching. Those disadvantages could be bypassed using microwave blanching. Three blanching methods (microwave, boiling water and steaming) were compared in this study in order to determine their effects on some functional properties of broccoli. In addition, the thermal damage on broccoli colour was evaluated. The effectiveness of each blanching process was performed measuring the lost of peroxidase activity, that results more rapidly in microwaves and steam treatments (50 and 60s respectively) than in boiling water treatment (120s). The colour indexes did not allow to discriminate a significant difference among treatments. The increase of treatment time caused a vitamin C decrease in samples blanched by boiling water and steam; this trend was not observed in microwaved samples. The phenols content did not significantly vary depending both on type and on time of treatment.

Effect of blanching on the dielectric properties and microwave vacuum drying behavior of Agaricus bisporus slices

The aim of this study was to assess the effects of hot water blanching (HWB) and microwave blanching (MWB) on the dielectric properties and microstructure of Agaricus bisporus slices before and after microwave-vacuum drying (MVD). A. bisporus samples subjected to MWB had the lowest dielectric constant (ε') and the highest dielectric loss factor (ε''), whereas the samples subjected to HWB had a relatively lower ε'' at 25 °C and 2450 MHz. MVD was applied effectively to the initial stages of drying A. bisporus slices when the moisture content was higher than 2.27 in dry basis (d.b.). The MVD duration of MWB samples was approximately 17.5 min, which was reduced by 22% compared with that of HWB samples. The micro-structure of the MVD-treated MWB sample was more uniform than that of the HWB sample. These results suggest that MWB improves the MVD process when applied to A. bisporus before drying.

The Effects of Microwave Blanching Conditions on Carrot Slices: Optimization and Comparison

The objectives of this study are (1) to determine conventional blanching (CB) conditions providing 100% peroxidase (POD) inactivation and adapt these inactivation conditions to microwave blanching (MB) for inactivating pectin methylesterase (PME); (2) to optimize the MB conditions by response surface methodology to ensure almost 100% PME; and (3) to compare the properties of samples at the optimum points with those of conventional blanched and unblanched carrot samples. CB conditions were found to be 300 s with 150 mL of blanching water at 94C. MB conditions of samples have been optimized by using independent variables: microwave power (360–900 W), blanching time (10–300 s) and blanching water volume (0–150 mL). Three optimum points were determined: (1) 900 W − 170 s − 75 mL water; (2) 630 W − 190 s − 75 mL water; and (3) 360 W − 300 s − 75 mL water for MB. PME inactivation ratio was determined as almost 100% optimum points. Therefore, pectin was highly retained, carotenoid contents and color values were better protected as well. In summary, 360 W/300 s/75 mL water conditions were found to be optimum for blanching of carrots. Practical Applications Nowadays, the food industry focuses on novel treatments for inactivating enzymes with minimum deleterious effects on texture, flavor and nutrients. Blanching is one of the preprocessing steps before canning, drying and freezing of vegetables. Blanching treatment also stabilizes color, texture, flavor and nutritional quality of the products, as well as inactivates peroxidase and pectin methylesterase which catalyzes deleterious changes. Microwave heating is a very popular food processing technique and can be utilized as an alternative to water blanching. This study explored whether microwave blanching can be used for enzyme inactivation, which, in turn, requires less processing time and water with minimal loss of quality.

MICROWAVE BLANCHING APPLICATIONS in FRUIT and VEGETABLE PROCESSING

Meyve ve sebze isleme sanayinde kullanilan geleneksel haslama yontemleri, uzun islem sureleri, yuksekislem maliyetlerinin yaninda urunlerin besinsel, duyusal ve teksturel ozelliklerinde bazi istenmeyenetkiler meydana getirmektedir. Son yillarda teknolojik gelismeler ile beraber tuketicinin hizli hazirlanangida tercihinin artmasi ile gida sanayi, urun kalitesini koruyarak, pratik ve dusuk maliyetli islemetekniklerine yonelmistir. Meyve ve sebze islemede de bu tekniklerin kullanilmasi ile uretim maliyetleridusurulerek verim artisi saglanmaktadir. Bunlardan biri olan mikrodalga, geleneksel yonteme alternatifolarak kullanilmaktadir. Bu derlemede mikrodalga haslama uygulamasinin enzim inaktivasyonu,toplam pektin, toplam karotenoid, renk, doku ve agirlik degisimi gibi bazi kalite ozelliklerine etkileriningeleneksel haslama uygulamasi ile kiyaslanmasi amaclanmistir. Sonuc olarak, mikrodalga haslamauygulamasinin minimal islem ozellikleri, enerji ve zaman tasarrufu, islem hizi, etkin enzim inaktivasyonuacisindan avantajlarinin yani sira, hizli isi degisimi nedeni ile urunlerde nem kaybina bagli agirlik azalmasive renk farkliliklari meydana getirdigi belirlenmistir

Comparison of Three Blanching Treatments on the Color and Anthocyanin Level of the Microwave-Assisted Spouted Bed Drying of Purple Flesh Sweet Potato

Browning and a serious drop in anthocyanin level occur during microwave-assisted spouted bed drying (MWSB) of purple-flesh sweet potato (PFSP) cubes. Blanching pretreatment inhibits browning and also affects the drying behavior. Effects of microwave blanching (MWB), hot water blanching (HWB), and steam blanching (SB) were examined experimentally. The results showed that MWB leads to rapid peroxidase (POD) degradation, reduces the drying time, and yields highest anthocyanin level after MWSB drying. However, the color of the dried product was not as bright and purple as those obtained by HWB and SB treatments. Microwave blanching can improve the MWSB drying process to maintain the anthocyanin level in dried products while reducing the drying time.

Effect of microwave blanching on the quality of frozen Agaricus bisporus.

The aim of this work was to determine the effect of microwave blanching on the levels of selected quality parameters in frozen Agaricus bisporus. Before freezing, mushrooms underwent one of the following treatments: blanching in water; blanching in a solution of sodium metabisulphite and citric acid; microwaving for 5 min; and combined blanching (first in water, then in a microwave oven). Products were freeze stored for 8 months at -25 ℃. Frozen storage resulted in decreased levels of vitamin B1, total polyphenols and antioxidant activity of 10-49%, as well as an increase in polyphenol oxidase activity compared with products immediately after freezing. The values for most colour parameters and whiteness intensity decreased, while cream, yellow, brown and grey saturation increased. There was a considerable deterioration in sensory quality, particularly colour. Microwave-blanched products had significantly higher dry matter, ash, vitamin B1 and B2 content than the remaining products as well as half the polyphenol oxidase activity. Total polyphenols and antioxidant activity were highest in the product blanched in the sodium metabisulphite solution, followed by the microwave-blanched product. Compared with the product blanched using sodium metabisulphite, microwave-blanched mushrooms showed slightly greater darkening but were superior in flavour and aroma.

Cyanidin-3-glucoside의 안정성을 향상시킨 오디즙 가공방법

오디의 기능성이 언론에 홍보됨에 따라 오디 소비 촉진 및 가공제품에 관한 관심이 증대되고 있으나 오디즙 가공시 기능성 물질인 C3G 색소의 안정성에 관한 기초자료가 없는 실정이다. 이러한 문제점을 해결하고 오디의 이용확대를 위해 항산화색소 C3G의 안정성을 향상시킨 오디즙 가공방법을 개발하였다. 그 결과를 요약하면 다음과 같다. 1. 오디와 서당의 비율을 1 : 1로 하여 용기에 담고 식품첨가제인 구연산을 0.3% 첨가하는 것이 C3G 함량과 항산화능을 향상시키는 가장 좋은 방법이다. 올리고당의 경우 구연산을 첨가하는 것이 오히려 항산화능을 떨어뜨리므로 사용하지 않는 것이 좋다. 자일리톨의 경우 가공방법 중 가장 낮은 C3G 함량을 나타냈으나 구연산을 첨가하면 색소함량과 항산화능을 향상시키므로 반드시 구연산을 첨가한다. 2. 보관용기(투명유리병, 갈색유리병, 알루미늄 호일, 녹색유리병, 반투명유리병)보다 구연산의 첨가가 항산화색소 C3G의 안정성에 영향을 미치는 것으로 판단된다. 3. 오디즙 가공시 전자렌지를 이용하여 3분간 blanching 하여 색소의 안정성에 관여하는 효소를 불활성화 시키는 방법은 항산화색소 C3G 함량을 다소 떨어뜨리므로 냉동오디를 그대로 사용하는 것이 바람직하나 항산화능에 있어서는 보존기간동안 타 처리구에 비해 안정화시키는 효과를 나타냈다. As mulberry fruit's functionalities are known to the media, the interest in promoting of consumption and processed products is increasing. But there is no C3G(Cyanidin-3-glucoside) data based on the stability of the pigment during processing. To solve this problems, and to expand the use of mulberry fruit, processing methods was developed for mulberry fruit juice improved cyanidin-3-glucoside(C3G) stability. The results obtained are summarized as follows. The food additive citric acid with 0.3 % improved C3G content and antioxidant ability in the treatment of mulberry fruit and sucrose the ratio of 50 % : 50 %(w/w). In the case of the addition of oligosaccharides, citric acid decreased antioxidant ability. Xylitol treatment showed up the lowest of C3 content, but by the addition of citric acid improved the pigment content and antioxidant activity of the mulberry fruit juice. Addition of citric acid was more affected C3G stability than containers (clear glass bottles, brown glass bottles, aluminum foil, green glass bottle, translucent glass bottles). In the processing of mulberry juice, 3 minutes blanching treatment using microwave dropped C3G content somewhat. Therefore, using this method is not recommended. However in the antioxidant ability, microwave blanching showed a stabilizing effect compared to the other treatments.

Comparison study of conventional hot-water and microwave blanching on quality of green beans

Microwave blanching of green beans (Phaseolus vulgaris L.) was explored as an alternative to conventional hot-water blanching. Batches of raw pods were treated similarly to an industrial process employing a hot-water treatment but using a microwave oven for blanching. The effects of microwave processing time and nominal output power on physical properties (shrinkage, weight loss, texture, and color), enzyme activities (guaiacol peroxidase, l-ascorbate peroxidase, and catalase), and ascorbic acid content of pods were measured and modeled by first-order kinetics. Inactivation of peroxidase (POD) was the best indicator to assess the efficiency of microwave-blanching of green beans. No significant differences in product quality were found between hot-water blanched and microwaved pods at optimal processing conditions. Furthermore, since shorter processing times and higher ascorbic acid retention were found, microwave processing of green beans can be a good alternative to conventional blanching methods.

Electromagnetic Radiation‐Based Dry Blanching of Red Bell Peppers: A Comparative Study

AbstractRetention of water‐soluble nutrients, prevention of solid loss and elimination of waste water generation are some of the advantages of dry blanching. Dry blanching of red bell pepper (Capsicum annuum L.) slices using infrared (IR) and microwave (MW) radiations was attempted and its performance was compared with conventional water and steam blanching methods. Processing conditions (time and temperature) were standardized on the basis of degree of enzyme inactivation (peroxidase, polyphenol oxidase). Effect of blanching methods on retention of micronutrients such as ascorbic acid, β‐carotene and protein, besides product shrinkage, structure and texture (shearing force) were analyzed. Water and steam blanching were found to need lower processing time (1.0 and 1.5 min, respectively) compared with IR (6.0 min) and MW blanching (3.0 min). However, MW‐blanched samples retained higher amounts of ascorbic acid (94.7%). Dry blanching with IR (150C) and MW (17.5 W/g) resulted in higher retention of β‐carotene (103.2 and 118.6%, respectively) compared with water (60.3%) and steam blanching (88.3%). Dry blanching resulted in moisture loss (1–6%) and shrinkage, perhaps resulting in higher shearing force observed in dry blanched slices. Scanning electron micrographs indicated that method of blanching has a role on extent of effect on cell structure.Practical ApplicationsRed bell pepper is a rich source of ascorbic acid and β‐carotene. This study explored the possibilities of dry blanching red bell pepper using infrared and microwave radiation as a potential alternative to water and steam blanching. The dry blanching is expected to retain higher amount of nutrients, reduce solid loss and eliminate effluent generation besides being convenient to operate.

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

SummaryThe 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.

Microwave blanching and drying characteristics of Centella asiatica (L.) urban leaves using tray and heat pump-assisted dehumidified drying.

The appropriate stage of maturity of Centella asiatica (L.) Urban leaves was investigated. Mature leaves with large diameter contained high total phenolics and % inhibition. Microwave blanching for 30s retained the highest total phenolics and the microwave blanching for 30s and 45s retained the highest % inhibition. Modified Henderson and Modified Chung-Pfost models showed the best fit to both fresh and blanched leaves for equilibrium moisture content, Xe = f(RHe, T) and equilibrium relative humidity, RHe = f(Xe, T), respectively. The Modified Page model was the most effective model in describing the leaf drying. All drying was in the falling rate period. The drying constant was related to drying air temperature using the Arrhenius model. Effective moisture diffusivities increased with increasing temperature and blanching treatments as well as dehumidification by heat pump-assisted dehumidified dryer. The heat pump-assited dehumidified drying incorporated by the microwave blanching could reduce the drying time at 40°C by 31.2% and increase % inhibition by 6.1%. Quality evaluation by total phenolics, % inhibition and rehydration ratio showed the best quality for C. asiatica leaves pretreated by microwave blanching and dried at 40°C in heat pump-assisted dehumidified dryer.

EFFECT OF BLANCHING TREATMENTS AND FROZEN STORAGE ON THE QUALITY ATTRIBUTES OF FROZEN ARTICHOKE

The aim of this study is to make Artichoke available all the year around and to compare the effect of blanching methods on the physical and chemical properties of the artichoke under study. Artichoke (Cynara Scolymus) Balady cv. was brought from Qaha Experimental Farm, Qalyoubia Governorate, and blanched within 10 hours of harvest. It was blanched by three methods. Conventional, boiling in 0.3%citric acid solution for a period of 2,4 and 6 minutes, Steam under atmospheric pressure for 10, 15, and 20 minutes. Bracts were heated in microwave using non rigid thermoplastic bags filled with 60 ml 0.3% citric acid solution for 2,3 and 4 minutes. The blanched bracts were cooled down, drained, packed in polyethylene pouches under vacuum, sealed, labeled, frozen at - 20oC and stored in deep Freezer at -18oC ±2 for six months .The effect of blanching treatment before and after being blanched on peroxidase activities, color ,firmness, ascorbic acid, dry matter, amino nitrogen and mineral contents including (Ca, P, Mn, Na, K, Fe, Zn, and Cu) were studied and discussed. This indicates better quality for Microwave blanched artichoke. Also, Changes in chemical composition of artichoke after being frozen and stored for six months were meagre . Also, changes in chemical composition as well as organoleptic properties of the frozen stored artichoke were evaluated after being cooked which indicates better quality for Microwave blanched artichoke that retained the greatest amount of ascorbic acid and had lighter appearance, good visual color, texture and flavor scores as revealed by the organoleptic panel test. The study indicated that the overall quality of Microwave blanched Artichoke was as good as or superior to boiling water and steam blanched vegetables. Microwave blanching is a suitable alternative to boiling water or steam blanching when preparing vegetables for home freezing .

Effect of blanching on microwave freeze drying of stem lettuce cubes in a circular conduit drying chamber

Effects of boiling water and microwave blanching methods on the dielectric properties, electrical conductivity as well as microstructure of stem lettuce cubes (as a model for plant tissue) were studied. The study also focused on how different blanching methods affect microwave freeze-drying (MFD) in a circular conduit drying chamber and conventional freeze drying (FD) of stem lettuce cubes. Results showed that the electrical conductivity of samples blanched by microwave was two times higher than that of boiling water blanched ones and five times higher than that of unblanched samples. Apart from that, dielectric constant (ε′) and loss factor (ε″) of the stem lettuce cubes decreased significantly after freezing. MFD duration of microwave blanched samples was approximately 4.5h, reduced by 30% compared to boiling water blanched ones. MFD process in a circular conduit yielded products of high quality compared to that in a tray.

Blanching of red beet (Beta vulgaris L. var. conditiva) root. Effect of hot water or microwave radiation on cell wall characteristics

The effect of enzymes inactivation through traditional (water, 90 °C) and microwave blanching (constant power of 350 W and changing power with values higher than 900 W) on cell wall polysaccharides as well as on microstructure of beet root tissue was studied with the goal of attaining a better understanding of the changes produced by treatment and its consequences on the functional properties of cell wall polymers. Powers higher than 900 W produced greater tissue microstructural damage due to alteration of the cell wall network. The contact between neighboring cells persisted after microwave treatment at 350 W while traditional blanching or blanching at higher microwave powers (90MW) produced separation of the middle lamella at different points and also cell separation was observed for the last mentioned treatment. The formation of entanglements of pectin-in-extensin in 350 W-treated beet root and the higher content of calcium and diferulated cross linked pectins in the case of traditional treatment may account for the better mechanical performance observed for these tissues. The microwaving at 350 W modified the cell wall polymers in such a manner that produced an increase in their hydrophilicity.

Microwave inactivation of red beet (Beta vulgaris L. var. conditiva) peroxidase and polyphenoloxidase and the effect of radiation on vegetable tissue quality

Abstract The inactivation of polyphenoloxidase (PPO) and peroxidase (POX) in red beet by traditional and microwave (MW) blanching was studied. Microwave heating effects on color and texture were also studied. Red beet subjected to MW blanching for 5 min at 100–200 W resulted in large weight losses accompanied by a high degree of shrinking. POX was the more heat resistant enzyme. The 90% destruction ( D value) of the activity of both enzymes could be achieved only at 200 W within the 5 min frame employed for the tests. When the samples were immersed in water and both the food sample and the water were submitted to MW exposure at 250–450 W or variable power with a maximum at 935 W, shrinking was avoided. The D value at 90 °C (reference; D T ref ) and z could be determined after time–temperature corrections, and it was observed that, in general, D T ref values for POX were smaller than for PPO. The microwave treatment (maximum power: 935 W) designed to provide a similar temperature profile to the one observed for traditional blanching (immersion in water at 90 °C), showed the smallest D T ref value for POX inactivation. All treatments reduced elastic characteristics and changed the color of the tissues showing a shift to blue mainly in the case of microwave processes.

EFFECTS OF BLANCHING ON GRAPES (VITIS VINIFERA) AND CHANGES DURING STORAGE IN SYRUP

ABSTRACT This paper studies the effects of conventional and microwave blanching on grapes that are being processed for storage in syrup. An analysis was made of the blanching effects on macro- and micronutrients, as well as on color and mechanical properties. To test the effectiveness of these blanching treatments, enzymatic residual activity was measured for polyphenol oxidase, peroxidase and pectinmethylesterase. Both blanching treatments reduced enzyme activity in the grapes, especially polyphenol oxidase (99%). Blanching treatments also caused significant decrease in tartaric acid (TA) also as in color and mechanical changes, more marked in conventional-treated samples. As for the effect of storage, microwave treatment supposed a greater stability of TA and total phenols than conventional one, also as a greater antioxidant activity of grapes. From this point of view, microwave treatment of samples immersed in water can be proposed as a good alternative to conventional heating in boiling water for grapes blanching. PRACTICAL APPLICATIONS Blanching is a relatively mild treatment, which aims to inactivate enzymes that would cause a decrease of final product quality. The microwave energy has attracted considerable interest because of the penetration capacity of waves, heating not only the food surface but also the inner part. This speeds up the drying process and contributes to improve the quality of the product. The results of this study showed that microwave blanching of grapes when immersed in water has advantages as compared with conventional treatment. Enzyme inactivation achieved with this kind of energy was very similar in both cases, but microwave treatment supposed a greater stability of tartaric acid and total phenols than conventional one, also as a greater antioxidant activity of grapes.

Blanching peppers using microwaves

Enzymatic reactions are not desirable in ripe fruits and vegetables. They cause losses along transportation, storage and processing. Blanching is a pre-treatment operation whose aim is to inactivate enzymes, and is usually applied before cutting, peeling, and freezing in order to avoid browning and changes in texture. Besides inactivating enzymes such as polyphenoloxidase, peroxidase and pectinase, blanching may induce sensory and chemical changes. The purpose of this work was to evaluate changes in antioxidant activity of Capsicum annuum Jalapeño type, when treating with microwaves to inactivate polyphenoloxidase. The whole fresh peppers (85% moisture) were blended until a paste was obtained. Ten grams portions were placed in a glass container and processed in a microwave oven until the inactivation of polyphenoloxidase was reached. Inactivation of the enzyme was confirmed with a spectrophotometric method using catechol as substrate. The processed peppers samples were mixed with 80% ethanol to extract phenolic compounds that were determined by the Folin Ciocalteu method. The antioxidant activity was evaluated using the radical ABTS, as described by Charurin et al (2002). Results showed that phenolic compounds were reduced from 9.6 to 7.6mg/ g peppers (dry weight basis) and antioxidant activity was enhanced from 29 to 42μM de trolox/ g peppers (dry weight basis) with thermal microwave blanching. Changes in the content of phenolic compounds were confirmed using high performance liquid chromatography, and the emergence of other phenol derivatives with enhanced antioxidant activity was detected in blanched samples. It may be concluded that blanching Jalapeño peppers with microwaves may induce the formation of derivatives of phenolics with enhanced antioxidant activity.