Massey Documents by Type

Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294

Browse

Filters

1977 - 197912010 - 20151

Settings

Has files: YesSubject: search.filters.subject.Freezing

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Effects of different freezing/thaw-ageing regimens on physicochemical, biochemical characteristics and meat quality attributes of lamb loins : a thesis presented to Massey for the partial fulfilment of the requirements of the degree of Masters of Food Technology, Massey University, Manawatū, New Zealand
    (Massey University, 2015) van der Stok, Carolijn Henrick Marie
    New Zealand red meat is in demand around the world; consumers recognise the safe, healthy, clean and green values of New Zealand’s pasture-raised beef lamb and venison. Meat is transported chilled in containers to overseas markets, and recently container ships have started to travel slower to reduce fuel consumption. This has resulted in the meat spending longer in the containers, meaning that key quality attributes of lamb cannot be guaranteed anymore. Finding an alternative method to provide the overseas consumers with chilled meat of the required quality is a top priority for the industry. Currently during container transport, meat is ageing for 6/8 weeks but with the newly introduced longer transport time to overseas markets it is too long for the meat in terms of food quality. Frozen meat is traditionally aged first before freezing. Previous observations show that 2 weeks ageing for lamb is enough to give equivalent quality attributes to the meat as ageing for 8 weeks. In the current study meat is frozen first and then thawed-aged and it was therefore hypothesised that by increasing the thawing-ageing temperature the ageing process could be accelerated. This thesis focused on determining the effects of different freezing/thawing-ageing regimens on meat quality and physical and biochemical characteristics of lamb loins. To study the effect of the different regimens, 10 treatments were set up and 90 loins in total have been used. The loins were randomly assigned to three different freezing conditions named Slow Freezing (SF), Fast Freezing (FF) and Very Fast Freezing (VFF) followed by three different thaw/ageing regimens: -1.5°C, 1°C and 3.5°C. A control group was included as treatment number 10, the Control group represents a non-frozen treatment with only 2 weeks of ageing. The effects on the quality of the loins were evaluated through the use of quality measurements such as pH, colour, water holding capacity, tenderness and lipid oxidation. Other analyses used to give an indication of the mechanisms for any quality differences were histology and metabolomics. The data suggest that FF and VFF resulted in a greater water-holding capacity and colour stability than SF. Ageing at 3.5°C showed a general trend for accelerated lipid oxidation compared with ageing at -1.5°C and 1°C. SF seems to contribute to damage along the fibre whereas FF and VFF show obvious holes within the fibres. These different types of damage may lead to lesser or varying meat quality. Overall, this work found that FF and VFF showed benefits over SF in several aspects of meat quality, but the differences were small. The results also suggest that FF or VFF could be used to avoid some of the common quality defects associated with freezing first and then thaw-ageing. This may potentially provide an opportunity for the New Zealand meat industry to utilise frozen storage/shipping and so saving money while still meeting the consumer demands for high quality fresh meat.
  • Thumbnail Image
    Item
    Heat transfer during freezing of foods and prediction of freezing times : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biotechnology at Massey University
    (Massey University, 1977) Cleland, Andrew Charles
    A study of methods for predicting the freezing time of foods was made. Four shapes - finite slabs, cylinders, spheres and rectangular bricks were considered. For each shape experimental measurements of the freezing time were made over a wide range of conditions using Karlsruhe test substance, a defined analogue material. Experiments with slabs of minced lean beef and mashed potato were also conducted. Practical food freezing problems, where the material is initially superheated above its freezing point and the third kind of boundary condition (convective cooling) is applied, have not been solved analytically because of the non-linear boundary conditions. Food materials when freezing release latent heat over a range of temperature which further complicates any attempt at solution. The accuracy of the various solutions to the freezing problem proposed in the literature was evaluated by comparison of the various calculated freezing times with the experimentally determined values over a total of 187 freezing experiments. For those solutions requiring numerical evaluation, the best was found to be a three-level finite difference scheme which generally gave a prediction of the freezing time to within ±9% of the experimental values with 95% confidence. With the regular geometric shapes investigated finite elements have no advantage over finite differences and were not considered. For the existing exact and approximate analytical solutions, it is shown that these do not give accurate prediction of the freezing time for any of the four shapes, mainly because all but two of these solutions do not take account of initial superheat in the material to be frozen, and these two solutions are for initial superheat in a semi-infinite slab, not a finite slab. For the existing empirically modified solutions and empirical relationships, it is shown that they do not give accurate prediction of freezing time; at best the 95% confidence limits of the percentage difference between the calculated and experimental freezing times are 0% to +20% for slabs, cylinders and spheres. All solutions for freezing of rectangular bricks with the third kind of boundary condition use the geometric factors derived by Plank. These factors are shown to be subject to error, the error increasing as the ratios of the two larger dimensions to the smallest increase. A group of formulae is proposed which are simple to use and give accurate prediction of freezing time. They modify the geometric factors in Plank's equation, taking initial superheat into account, and in the case of rectangular bricks correct the errors inherent in these geometric factors. This group of simple formulae are shown to predict the freezing time with 95% confidence to within 5% of the experimental values for slabs, to within 7% for cylinders and spheres, and to within 10% for rectangular bricks. The prediction accuracy of the simple formulae and the three level finite difference scheme are similar but the simple formulae can be calculated quickly without the use of a computer which is a big advantage. In addition to simplicity and accuracy the simple formulae are also versatile, and by use of suitable approximations can handle some practical problems in which conditions change with time.