Sterilization solutions for aseptic processing using a continuous flow microwave system

Modeling time-temperature history and sterilization value of mango puree under conventional and microwave assisted pasteurization

Continuous pasteurization of liquid foods has to provide the desired lethality level to guarantee food safety with minimum degradation of quality attributes (sensorial and nutritional characteristics) and high energy efficiency. To optimize quality and cost, a thermal process should be modeled considering flow, heat transfer and mass dispersion principles; however, flow through helical tubes and microwave heating require a complex 3D multiphysics approach. Herein a simplified 2D approach is presented to model a hybrid pasteurization unit with conventional and microwave heating under laminar flow to predict axial and radial distributions of temperature and residual activity of a microorganism or enzyme. A study case of 20 °Brix mango puree (power law fluid) processing is used to test the model based on an existing pilot plant unit. Results were useful to compare conventional and microwave heating regarding the process sterilization value and model can be used for process analysis, design and optimization.

Effect of microwave-assisted processing on polyphenol oxidase and peroxidase inactivation kinetics of açai-berry (Euterpe oleracea) pulp

Microwave heating has been considered a promising technology for continuous flow thermal processing of fluid foods due to better retention of quality. Considering the importance of açai-berry pulp and its perishability, the inactivation kinetics of peroxidase (POD) and polyphenol oxidase (PPO) were investigated under conventional and microwave heating. First-order two-component model was well fitted to the data, indicating the presence of at least two fractions with different resistances. POD was more thermally resistant (90% inactivation for 40 s at 89 °C) and could be considered as a processing target. Inactivation curves dependency on heating technology suggests specific effects of microwaves on the protein structure. Additionally, the dielectric properties of açai-berry pulp were evaluated at 915 and 2,450 MHz for temperatures up to 120 °C. Power penetration depth dropped with temperature at 915 MHz (from 29 to 11 mm), but was less affected at 2,450 MHz (between 8 and 11 mm).

Improving the quality of vegetable foodstuffs by microwave inactivation

With the aim of improving the loss of quality in retorted vegetables, experiments on pretreatment inactivation using microwaves were carried out to allow the heating intensity to be reduced during retorting. Microwave heating reduced the bacteria level by 10³ CFU/g, and was a more effective method considering the short processing time of 3 min and the required energy being 70-80% of that when using steam. The inactivation effect was due to dielectric heat generation by the high-frequency microwaves. The inactivation effect for heat-resistant Bacillus amyloliquefaciens was indicated by a reduction of 10² CFU/g after 3 min of microwave heating. The total bacteria counts for peeled potato and spicy sauce with vegetables decreased by 3-4 log CFU/g after 3 min using microwaves, and heat-resistant microorganisms were reduced by 2 log CFU/g. Combining microwave heating and mild retorting is expected to produce higher quality vegetable foodstuffs compared to conventional retorting.

Dielectric Properties of Infant Formulae, Human Milk and Whole and Low-Fat Cow Milk Relevant for Microwave Heating

The dielectric properties of three different reconstituted infant formulae, human milk, as well as, whole and low-fat pasteurized cow milk were measured at temperature interval from (5 to 70) °C and at frequency of 2450 MHz. The dependency of the dielectric properties with temperature is presented. The values of penetration depth were determined and can be used to estimate the ideal bottle-feeding or container diameter to use in a domestic microwave oven or specific microwave equipment to pasteurize human milk in Human Milk Banks (HMB).

Concentration-related microwave heating processes: electromagnetic interference of Maillard reaction substrates (glucose and lysine)

Glucose and lysine are important substrates involved in the Maillard reaction.

Levantamento das distribuições de temperatura em leito de arroz com casca durante o tratamento térmico por micro-ondas

Durante o aquecimento dielétrico, a distribuição do campo elétrico dentro de uma cavidade ocorre a partir de uma propagação multimodal, ocasionada por inúmeras reflexões das micro-ondas provenientes das paredes metálicas da cavidade. Essas reflexões múltiplas geram regiões de maior e menor intensidade de campo elétrico no espaço e, por consequência, um aquecimento não uniforme no produto. O objetivo deste estudo foi o levantamento dos valores de temperaturas obtidos durante o tratamento térmico por micro-ondas em um leito de arroz em casca úmido posicionado em um porta-amostra, dentro de uma cavidade que apresenta uma geometria prismática de seção sextavada. A cavidade foi desenhada para, operando em frequência de 5,8 GHz e potência máxima de 700 W, minimizar a heterogeneidade de distribuição das intensidades do campo elétrico, gerando um aquecimento mais uniforme do produto. Verificou-se que as diferenças de temperatura registradas pelos sensores no leito de arroz foram de 3,2 °C a 12,5 °C durante os tratamentos térmicos estudados. Não foi observado um comportamento padrão que indicasse uma região de maior aquecimento em relação à altura e direção radial do leito de arroz durante os tratamentos térmicos por micro-ondas

Microwave Food Processing

Consumers prefer food products with enlarged shelf life, which are quick to prepare, healthy and fresh like. Traditional food processing methods are based on intensive heating and as a result cause quality loss. Minimal processing techniques such as microwaves approach consumer's demands to create fresh like products with enlarged shelf life. Microwave technology can be very useful for food processing, because products are heated directly instead of conventional heating by convection and conduction. This means a reduction of the total processing time, no overheating on the outside of the product, and preservation of the fresh product quality. This chapter presents a complete picture of current knowledge on application of microwave in food processing which has been used for different processes like blanching, sterilisation, thawing, drying and extraction of various products. In many cases combinations with microwaves gave the best results.