Abstract Empirical models can be used to represent the recrystallization process in frozen food as a simple strategy (limited by the complexity of the process). Anyway, the empirical model has a better fit when used within the range of experimental values from which they were generated. In this work, an empirical mathematical model derived from the Arrhenius equation was proposed, since in previous publications it was shown that there is a direct relation between the growth of ice crystals and the temperature oscillations that occur during the storage of frozen products. Equivalent diameter data of ice crystals obtained from the storage of frozen Tilapia analyzed in the optical microscope was used as a database for the formulation of the empirical model. The developed model was acceptable to predict ice crystal growth during recrystallization in frozen Tilapia samples and had the advantage of being simple and robust enough to estimate this growth in the flotation range from -18 to -11 °C After the first 30 days of storage. The average equivalent diameter (Deq) values predicted by the model indicated that the model provides a satisfactory description of the growth of the crystals with R2 equal to 0.930.

ABSTRACT A comparative test of water heating between the hybrid system - solar collector with heat pump - and a system with conventional supplementary heating - with high electric power - was performed. For this, a small capacity heat pump was installed, which was later installed together with a solar heating system, composed of a 250 L thermal reservoir and three thermoplastic collector plates. Tests were carried out to evaluate the COP of the heat pump and the energy consumption of the solar heating system operating with the heat pump and with an electrical resistance of 3000 W. In the laboratory tests, the heat pump presented an average COP of 2.15. In the field tests, the energy consumption of the solar system with heat pump was 54.9% lower when compared to the tests in which electrical resistance was used as a source of supplementary heating.

Abstract The degenerative effect of temperature fluctuations during storage time is a critical condition that needs to be quantitatively characterized in products where drip losses are appreciable. In this work, real storage conditions were reproduced using freezers modified to cause 3 levels of temperature fluctuation (± 0, ± 3, ± 5; ± 7) during storage of Tilapia (Oreochromis sp), at temperature of –18 °C. The fast frozen tilapia muscle (freezing cabinet) was chosen to quantify the growth of ice crystals according to temperature fluctuations. The identification of crystals in the optical microscope as well as histological treatments and measurements using specific software has shown that the growth of ice crystals in the first days of storage follows an asymptote, whose final value is conditioned only by the level of temperature fluctuations regardless of initial diameter, which begins storage. It has also been found that the growth of crystals formed during rapid freezing rapidly develops according to temperature fluctuations to which the product has been subjected. This work also identified statistically significant differences in the equivalent diameter of crystals formed at the four proposed levels of temperature fluctuation with significance level of p < 0.05.

O objetivo deste trabalho foi monitorar as condições operacionais do transporte frigorificado urbano de alimentos resfriados e congelados durante as entregas dos produtos e avaliar a influência das aberturas das portas da câmara nas alterações das temperaturas internas do ambiente frigorificado. Instrumentou-se uma câmara frigorífica bipartida do tipo ¾ com sensores de temperatura e pressão, que foram instalados em pontos específicos no sistema de refrigeração e nas superfícies internas e externas da câmara do caminhão. Após as monitorações, foi verificado que as aberturas de portas no momento das entregas resultaram na elevação da temperatura interna da câmara acima dos valores recomendados para a conservação adequada dos produtos transportados, além de que o aumento no número de aberturas de porta provocou um efeito acumulativo de aumento da temperatura interna, principalmente no compartimento de resfriados. Concluiu-se que o sistema de refrigeração utilizado pela frota de caminhões da empresa que produziu os alimentos transportados apresenta limitações quanto à manutenção da temperatura interna da câmara durante a rotina real de distribuição, pois não possui capacidade instantânea suficiente para retomar a temperatura adequada entre as entregas.

The objective of this work was to monitor the operational conditions of the transport of chilled and frozen foods during delivery within cities and to evaluate the impact of the door openings on the alteration of the internal temperature of the refrigerated environment. Several temperature and pressure sensors were used in a refrigerated container with two compartments and they were installed in the refrigeration system unit and on the internal and external surfaces of the container. After the monitoring tests, it was verified that door openings during deliveries resulted in a disturbance that raised the internal temperature of the refrigerated container above values recommended for adequate conservation of the products transported. Moreover, increasing the number of door openings promoted a cumulative effect on the internal temperature, mainly in the chilled food compartment of the container. It was concluded that the refrigeration system unit presented serious limitations with regard to the maintenance of the container's internal temperature during the actual distribution routine, since it does not possess enough instantaneous capacity to restore the temperature set-point between deliveries.

O congelamento de cortes de frango em túneis convectivos é normalmente realizado com o produto envolto por filmes de polietileno de baixa densidade (PEBD, embalagem primária) e acondicionado em caixas de papelão (CP, embalagem secundária). O objetivo deste trabalho foi avaliar o efeito da embalagem secundária no congelamento dos cortes de frango. Para isso, compararam-se as curvas de congelamento do produto processado acondicionado em caixas metálicas perfuradas (CMP), que praticamente eliminam a resistência térmica da embalagem secundária, com as curvas de congelamento do produto nas CP. Os ensaios, realizados em uma planta industrial de processamento de aves, indicaram que as CP possuem uma grande resistência térmica e que a substituição delas por PMB pode resultar em maior homogeneidade espacial do processo de congelamento e em tempos de processo 45% inferiores. A duração do patamar de temperaturas que caracteriza a etapa de solidificação foi sensivelmente reduzida, o que favorece a obtenção de produtos congelados de melhor qualidade. A aparência dos produtos congelados em CMP não foi afetada, devido à proteção oferecida pelo PEBD. Assim, a substituição das caixas de papelão por caixas metálicas perfuradas pode ser uma excelente alternativa para reduzir o tempo de congelamento e melhorar sua homogeneidade espacial em túneis industriais.

Freezing of poultry cuts in continuous convective air blast tunnels is normally performed with the products protected by Low Density Polyethylene (LDPE) as a primary packaging and using Corrugated Cardboard Boxes (CCB) as secondary packaging. The objective of this work was to investigate the influence of these secondary packaging on the freezing of poultry cuts in continuous convective air blast tunnels. The study was performed by replacing CCB with Perforated Metal Boxes (PMB) in order to remove the packaging thermal resistance. The assays, performed in a industrial plant, demonstrated that CCB used commercially for meat freezing have a high heat transfer resistance. Their replacement with PMB can lead to shorter freezing times and spatially homogeneous freezing. Reductions of up to 45% in the freezing times were observed using PMB. The plateau of the temperature curve, related to the freezing time of free water, was significantly reduced using PMB, which is accepted to lead to better product quality after thawing. As the products were protected by the LDPE films as primary packaging, their appearance were not affected. The results presented in this work indicate that replacing CBB with PMB can be an excellent alternative to reduce freezing time and improve freezing homogeneity in industrial air blast tunnels, which could also be applied to other products.

O comportamento reológico do açúcar líquido invertido com inversão de 59,68% e 89,88% foi estudado experimentalmente nas temperaturas de 17°C a 65°C, utilizando um reômetro rotacional de cilindros concêntricos. Os resultados mostraram que o açúcar líquido invertido apresenta comportamento Newtoniano na faixa de temperatura estudada. O efeito da temperatura na viscosidade foi expresso por relações do tipo Arrhenius, cujos coeficientes de correlação foram superiores a 0,99 e as energias de ativação apresentaram valores de 70,5kJ.mol-1 e 86,5kJ.mol-1 para as soluções com inversão de 59,68% e 89,88%, respectivamente.

The rheological behavior of invert liquid sucrose with two different percentages of inversion (59.68% and 89.88%) was studied from 17°C to 65°C using a concentric cylinders rheometer. The results showed that the invert liquid sugar exhibits Newtonian behavior within the range of temperature tested. The effect of temperature on viscosity of invert sugar was expressed by the Arrhenius relationship and the fitted models presented correlation coefficients (R²) greater than 0.99. The activation energies calculated for both samples, 59.68% and 89.88% of inversion, were respectively 70.5kJ.mol-1 and 86.5kJ.mol-1.