Effect of microwave power and blanching time in relation to different geometric shapes of vegetables
Introduction
Blanching is a mild heat treatment widely applied in food industry prior to freezing, canning or drying fresh vegetables and fruits (Ranjan, Dasgupta, Walia, Chand, & Ramalingam, 2017) in order to extend the shelf life of the products, stabilizing their nutritional quality and texture. This unit operation is mainly aimed to inactivate both microorganisms and quality changing enzymes responsible for deterioration reactions that contribute to off-flavors, odors, undesirable color and texture, and breakdown of nutrients (Manpreet, Shivhare, & Ahmed, 2000; Xiao et al., 2017).
Among the naturally occurring enzymes, peroxidase (POD) is used in the food industry as an indicator of blanching adequacy, due to its high thermal resistance (Ramesh, Wolf, Tevini, & Bognár, 2002). Based on the type of technique applied, blanching can be categorized as: i) wet blanching, which is achieved by dipping vegetables in hot water, hot solutions (containing acids and/or salts) or steam (Kidmose & Martens, 1999); ii) dry blanching, which is carried out using microwaves (MW) (Ramesh et al., 2002), infra-red radiation (Kalathur, Girish, & Hebbar, 2013) or high pressure (Castro et al., 2008).
In the last decade, the increasing consumer demand of minimum treated and fresh-like products lead food industries to the application of novel technologies for inactivating enzymes with minimum deleterious effects on texture, flavor and nutrients (Aziz, Mahrous, & Youssef, 2002; Demirdöven & Baysal, 2008). MW blanching (MWB) is of great interest for both academic and industrial point of view, and it has been applied on different vegetables such as potatoes (Severini, Baiano, De Pilli, Romaniello, & Derossi, 2004), broccoli (Eheart, 1967), carrots (Soysal & Söylemez, 2005), and bell peppers (Ramesh et al., 2002). In comparison with conventional wet blanching, MWB allows: i) greater nutrients retention due to the reduction of leaching losses during treatment; ii) faster heating rate (heat is internally produced, whereas in conventional blanching heat is transferred by conduction from the product surface to the inner part); iii) greater penetration depth; iv) space savings because the equipment takes up a smaller area (Benlloch-Tinoco, Igual, Rodrigo, & Martínez-Navarrete, 2015).
As described in literature (Chavan & Chavan, 2010), the effectiveness of MWB depends on: i) process conditions [i.e. MW frequency and power, heating speed, mass and mobility of the product inside the oven (rotation/non-rotation)]; ii) vegetable characteristics [i.e. dielectric properties, penetration depth, moisture content, density, physical geometry (size, thickness, shape), surface to volume ratio and specific heat]. The non-uniform temperature distribution during MW heating has been extensively studied (Geedipalli, Rakesh, & Datta, 2007; Gunasekaran & Yang, 2007; Manickavasagan, Jayas, & White, 2006; Vadivambal & Jayas, 2010) and several researchers have developed mathematical models in order to predict temperature distribution in the MW heated food (Campanone & Zaritzky, 2005; Ni & Datta, 1999; Vilayannur, Puri, & Anantheswaran, 1998; Yang & Gunasekaran, 2004). Among these, Van Remmen, Ponne, Nijhuis, Bartels, and Kerkhof (1996) tweaked simple models in order to obtain a qualitative prediction of temperature distributions in three basic geometries (i.e. sphere, cylinder and slab) for MW energy penetration in food products.
Brewer and Begum (2004) proved that microwave power levels applied for different times affected POD inactivation in broccoli, green beans and asparagus. Despite these researches on MWB, no studies have yet been carried out changing both the process parameters and the geometry of vegetable matter. Therefore, the aim of this study was to evaluate the efficacy of MWB, in terms of POD inactivation, applying various process conditions (i.e. MW power and process time) to different vegetables namely potato and leafy vegetables (savoy cabbage and white cabbage) mimicking the most common geometric shapes and assess the effect on selected quality attributes.
Section snippets
Sample preparation
Potatoes (Solanum tuberosum L. var. agria), savoy cabbage (Brassica oleracea L. var. sabauda) and white cabbage (Brassica oleracea L. var. capitata) were purchased from a local supermarket and stored in a refrigerator at 4 °C. Before the experiments, the samples were taken out and equilibrated to room temperature (25 °C) overnight. Potatoes were washed, hand-peeled, and cut into cylindrical- and cuboid-shaped. The cylinder samples (Cy) had a diameter of 24 mm and a height of 9 mm. For
Peroxidase inactivation
POD inactivation achieved by MWB, carried out applying various process conditions, is inferred by the colorless areas in potatoes and leafy vegetables, as shown in Fig. 1. For all MW powers applied, and in both cylindrical- and cuboid-shaped potatoes the POD inactivation was initially achieved at the core of the sample and it gradually extended toward the periphery with the increase of process time, following the temperature profile described in literature for MW heating (Chen, Collins,
Conclusion
During microwave blanching (MWB) of vegetables (potatoes, savoy cabbage and white cabbage), the simultaneous effect of the process conditions (i.e. MW power and process time) and the geometric shape (cylindrical, cubed, parallelepiped and slabbed) was evaluated testing the peroxidase (POD) inactivation and the firmness as indirect measure of the structural modifications.
In all the 3-D geometric shapes, POD inactivation was initially achieved at the core of the sample and gradually extended
References (40)
- et al.
Effect of gamma-ray and microwave treatment on the shelf-life of beef products stored at 5 °C
Food Control
(2002) - et al.
Comparison of microwaves and conventional thermal treatment on enzymes activity and antioxidant capacity of kiwifruit puree
Innovative Food Science & Emerging Technologies
(2013) - et al.
Superiority of microwaves over conventional heating to preserve shelf-life and quality of kiwifruit puree
Food Control
(2015) - et al.
Mathematical analysis of microwave heating process
Journal of Food Engineering
(2005) - et al.
Effect of thermal blanching and of high pressure treatments on sweet green and red bell pepper fruits (Capsicum annuum L.)
Food Chemistry
(2008) Effect of microwave vs water blanching on nutrients in broccoli
Journal of the American Dietetic Association
(1967)- et al.
Modeling the heating uniformity contributed by a rotating turntable in microwave ovens
Journal of Food Engineering
(2007) - et al.
Effect of experimental parameters on temperature distribution during continuous and pulsed microwave heating
Journal of Food Engineering
(2007) - et al.
Peroxidase and lipoxygenase inactivation during blanching of green beans, green peas and carrots
Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology
(1993) - et al.
Microwave inactivation of red beet (Beta vulgaris L. var. conditiva) peroxidase and polyphenoloxidase and the effect of radiation on vegetable tissue quality
Journal of Food Engineering
(2012)
Blanching of red beet (Beta vulgaris L. var. conditiva) root. Effect of hot water or microwave radiation on cell wall characteristics
Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology
Inactivation kinetics of peroxidase in zucchini (Cucurbita pepo L.) by heat and UV-C radiation
Innovative Food Science & Emerging Technologies
Comparison study of conventional hot-water and microwave blanching on quality of green beans
Innovative Food Science & Emerging Technologies
Kinetics and inactivation of carrot peroxidase by heat treatment
Journal of Food Engineering
Effect of simultaneous infrared dry-blanching and dehydration on quality characteristics of carrot slices
Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology
Recent developments and trends in thermal blanching – a comprehensive review
Information processing in agriculture
Comparison of temperature distribution in model food cylinders based on Maxwell's equations and Lambert's law during pulsed microwave heating
Journal of Food Engineering
Effect of microwave pretreatment on the kinetics of ascorbic acid degradation and peroxidase inactivation in different parts of green asparagus (Asparagus officinalis L.) during water blanching
Food Chemistry
The effects of microwave blanching conditions on carrot slices: Optimization and comparison
Journal of Food Processing and Preservation
Effect of microwave power level and time on ascorbic acid content, peroxidase activity and color of selected vegetables
Journal of Food Processing and Preservation
Cited by (20)
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
2022, Innovative Food Science and Emerging TechnologiesBlanching in the food industry
2022, Thermal Processing of Food Products by Steam and Hot Water: Unit Operations and Processing Equipment in the Food IndustryRadio frequency energy inactivates peroxidase in stem lettuce at different heating rates and associate changes in physiochemical properties and cell morphology
2021, Food ChemistryCitation Excerpt :POD, an enzyme belonging to the oxidoreductase class, has been proved to present better thermal stability than other enzymes in vegetables (Gonçalves, Pinheiro, Abreu, Brandão, & Silva, 2010; Ruiz-Ojeda & Peñas, 2013). For this reason, the residual POD activity is often selected to evaluate the adequacy of blanching treatment (Liburdi, Benucci, & Esti, 2019). Conventional blanching by hot water can effectively inactivate enzymes, but also has adverse effects on the color and texture of the fruits and vegetables (Gong et al., 2019; Guida et al., 2013).
Effects of different cooking techniques on bioactive contents of leafy vegetables
2020, International Journal of Gastronomy and Food ScienceCitation Excerpt :Microwave cooking has a wide range of applications in food processing. The applications of microwaves include drying, sterilization, pasteurization, thawing, and baking of food materials (Metaxas and Meredith, 1983; Gupta and Wong, 2007; Mondal et al., 2019; Liburdi et al., 2019). Microwaving is now a very popular cooking technique because of its ability in achieving high heating rates, reduction in cooking time, safe handling, ease of operation, and low maintenance (Salazar-González et al., 2012; Zhang et al., 2006).