Christina Skjöldebrand

Microwave heat treatment of apple before air dehydration : Effects on physical properties and microstructure

Abstract Golden delicious apple cubes were heated with microwave energy of high intensity (20 W/g), as a pre-treatment before air-dehydration at 40°C, 60°C and 80°C. After the microwave treatment extending for 0.75 up to 5 min, the cubes were finish-dried with only forced air at 2 m/s. Dehydrated and rehydrated samples were analysed with a puncture test using a texture analyser. The microstructure of the samples was studied with confocal laser scanning microscopy (CLSM). Dried apple pieces were harder and more shrunk when pre-treated with microwaves, compared to only air dehydration. Despite the shrinkage and increased firmness, the rehydration capacity of microwave “blanched” apple cubes was higher than when they were only air-dehydrated. Image analysis of the rehydrated apples showed that large voids (up to 0.5 mm in diameter) had developed, and that these increased with air temperature. Higher magnification of the images revealed cell separation and disruption of cell walls, caused by the microwave heating.

Impact of impingement on cooking time and food quality

Abstract An experimental study has been made, with the objective to find the impact of directed forced convection (impingement) on food quality. Two different foods were chosen for the study, yeast buns (representing category bread) and pork cutlet (representing meats). The tests were made in an experimental oven intended for the domestic market. The main results were a shorter cooking time and more uniform browning for meat (a reduction by up to 50% at similar air temperature as recommended). For smaller pieces of meat, browning was a general problem, as centre temperature increased to rapidly, at the air temperatures tested here. Buns were slightly more uniform in browning on the surface. The cooking time was basically similar to a traditional oven, but at much lower air temperature setting.

Reheating characteristics of crust formed on buns, and crust formation

Abstract The idea of this paper to examine some characteristics of crust formation during baking of yeast leavened dough. The aim is to find the impact of the crust on the heat and mass transfer rates. In a second test series, buns were baked under different conditions, and the rate of crust browning and thickness evolution was followed. The aim was further to see whether a baking at 145 °C under high convective boundary conditions could match traditional baking (hot air at 175 °C and top–bottom at 200 °C). Ready baked buns were reheated some with and some without (peeled off) crust. The results show a difference in heating behaviour. The temperature in buns heated with crust rose faster and levelled off at significantly higher temperatures than in buns without crust. The buns heated without crust lost weight at a rate about three times that of buns with crust. Air temperature and velocity influenced the loss rate for both kinds of buns. For the comparative study, it was found that although the internal heating rate of the buns was similar for the three heating technologies, the crust browning was faster and greater in the traditional processes. It was also found that the rate of browning is not significantly increased by impingement, even when varying the air velocity.

NIR-measurements of moisture changes in foods

Mass transfer and especially the movement and loss of water are important for the quality of cooked foods. Measurements of the water content changes during cooking are therefore valuable when it comes to controlling cooking processes. A near infrared reflection fibre optic probe is here used to measure water content changes inside pork meat and buns during heating. The results are compared with a moist porous brick (in the following called model food). Five different periods were seen locally in the centre. First a period of constant water content, then a period of constant decrease (constant rate period). The constant rate was followed by a period, an intermediate period where the temperature levelled at 100°C, while the water content decrease was small. In the fourth period the slope of the water content vs time curve became steeper and the temperature began to increase above 100°C. Finally, the water content moved to zero while the temperature rose towards the air temperature. The results for buns indicated that the water content near the surface began to decrease almost instantly and continued for the whole heating time in a falling rate manner. At the centre, the water content fell initially and then levelled. The major difference compared to the model food was the levelling off temperature, roughly 100°C in the food and 75°C in the model food.

Risk Management and Quality Assurance through the Food Supply Chain – Case Studies in the Swedish Food Industry

Processed food and eating out of the home are increasing phenomena, which presents new business opportunities for food manufacturers. However, the new food products require increased quality and safety, and thereby a more controlled distribution. The overall purpose of the research presented in this article is to describe the food supply chain from a critical context point of view in order to highlight the risks and the traceability issues. The paper expands previous discussions regarding critical control points into a critical context perspective in traceability in food supply chains. The initial part of the study is based on a literature review in the area of traceability combined with a number of related search words. A number of case studies have been carried out in order to map the food supply chains and better understand consumer standpoints. This paper describes how the system for distribution of food from manufacturer to end-user operates in Sweden. The chains studied all showed critical contexts. The paper suggests attitudinal changes towards overall supply chain responsibility, better resource utilisation and increased knowledge among actors. Furthermore it suggests supply chain actors to better integrate consumer insights on food safety perceptions in order to create value. (Less)

A computer simulation program for evaluation of the continuous heat treatment of particulate food products. Part 2: Utilisation

Abstract A computer program for calculation of temperatures in a liquid containing particles during continuous heat treatment has been developed at the SIK. The program facilitates the study of the influence of processing on product quality in an aseptic processing system. The calculated F value is related to the safety, and the cook value (C value) is related to the quality of the product. In this paper, results of some calculations using the program are presented. They concentrate on the influence of the processing conditions on the process design. These results indicate that factors such as particle heat transfer coefficient, both in the holding tube and in the scraped surface heat exchangers (SSHEs), flow conditions, particle diameter and sterilisation temperature have consequences for the holding tube length, i.e. the processing time, for a given lethality. For example, for small particle heat transfer coefficients ( 2 K), a small change will have a large effect on the required processing time (i.e. the holding tube length). However, at particle heat transfer coefficients > 150–200 W m 2 K a small change does not greatly affect the processing time (i.e. holding tube length). The program can thus be used to examine whether the surface heat transfer coefficient is the rate-limiting factor, or whether the heat conduction inside the particles is more important in the design of the process.

Water transport in meat during reheating

Abstract A study of heat and water transport in meat during a heating process was conducted. The meat samples were heated from 10 to 10 °C in a conventional oven at 175 °C and local water content and temperatures were measured during the heating process. Using whole meat from bovine muscles, the mechanism behind water transport inside the sample during heating was investigated. The anisotropy of meat in terms of heat and water transport was also studied. The study yielded two main results: When heating commences, water moves towards the centre of the samples. At a centre temperature of ~ 70 °C, water transport stops and changes direction. A theory for transport phenomena has been developed and is described in this paper. The results also indicate that, as expected, both water transport and heat transport are faster parallel to the meat fibres than perpendicular to them.

Method and instrument for measuring local water content inside food

A new method of measuring local water content inside food during heat processing has been evaluated. The method uses a fibre optic NIR-Instrument. The evaluation was mainly based on investigations of the influence of structure and temperature. The instrument was found to be very sensitive to both the structure and the temperature of the sample. The dependence on the temperature of the sample can be incorporated into the calibration and is thereby not an impediment to the measurements. The structural dependence makes quantitative measurements at different places in the sample difficult for inhomogeneous materials. However, measurements of dynamic changes in the water content in one spot work well for both homogenous and inhomogeneous materials and are probably the best application of the instrument. By using two or more optic fibres, the diffusion of water can also be measured.

Optical properties of bread in the near-infrared range

Abstract This paper reports on a method for determination of the optical properties of bread. The optical properties of white bread have been studied. The measurements were carried out for dough, crumb and crust. The transmission and reflection measurements were made with a Beckman spectrophotometer with an integrating sphere. Transmission functions and penetration depths were calculated and compared with previous investigations made at this institute (SIK). The influence of peak power wavelength and spectral range (800–1250 nm and 1250–2500 nm) on the penetration depth for crust and crumb have been determined. This study has shown that it is possible to calculate penetration depth for any radiator using transmission data in the range 800–2500 nm.

Moisture Content Distribution and Moisture Diffusion in Foods During Heating

“The mechanism of drying has been the subject of scientific study for more than 100 years, but it is still not thoroughly understood. External factors such as air temperature, pressure, humidity and velocity are governed by relatively simple and well known laws, but not the internal transfer of moisture.” Although Van Arsdel wrote this in 1973, the internal transfer of moisture is still not fully understood. One of the reasons for this is that until now there has been no way to measure the local water content inside a sample during a drying or heating process. A special fibre optic instrument has now been developed at SIK to measure the local water content, however. This instrument has been used in this project, in which the water transport in meat during heating has been studied, particularly in terms of the influence of meat fibre direction.