Development and predictive modelling of set yoghurt as a made-in-transit (MIT) product : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand
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Date
2013
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Massey University
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Abstract
The manufacture of food during distribution, a concept known as “made-in-transit”
(MIT) manufacture, has the potential to expand the distribution reach, extend shelf-life, and
provide the customer with the freshest possible product. Benefits for the manufacturer
include maximising throughput while minimising manufacturing space and inventory. This
concept is new, with mushrooms being the only MIT food developed so far. In this study, the
feasibility of developing an MIT product from a fermented food was determined using set
yoghurt as a model system. An MIT yoghurt was developed through the alteration of some of
the yoghurt manufacturing parameters (e.g. milk base formulation, heat treatment, starter
culture composition and fermentation temperature), extending the yoghurt fermentation
time from about 4 h to 168 h (7 days). It was found necessary to fortify the milk base
(reconstituted skim milk powder) with a suitable protein-containing dairy ingredient (sodium
caseinate and milk protein concentrate were found best) to rectify the poor texture of the
resulting yoghurt. Descriptive testing and acceptance testing using trained and consumer
sensory panels, respectively, showed that MIT yoghurts were significantly different from
conventionally made yoghurt, but were more acceptable. The yoghurts were found to have
adequate shelf lives post fermentation, partly owing to the use of ultra-high temperature
(UHT) sterilization of the yoghurt milk base prior to inoculation to ensure the absence of
starter bacteria competitors. As the production of MIT yoghurt involves a relatively long,
temperature dependent fermentation, it was considered useful to develop models for
predicting the effects of both time and temperature on such dependent variables as starter
bacteria count, pH, and firmness. A predictive microbiology approach was taken. The modified
Gompertz equation was found to model adequately the time dependence of starter bacteria
growth and firmness development during fermentation, while the modified logistic equation
was found adequate for modelling pH decline. These two equations are primary models,
whose parameters were then related to temperature using the square root (Ratkowsky)
equation as a secondary model. Combination of the primary and secondary models provides
means of predicting the effects of both time and temperature simultaneously. Comparison of
predictions with data generated in extrapolation and interpolation experiments proved the
efficacy of the models.
The work described in this thesis demonstrates the potential of the MIT concept for a
fermented food. The concept could be applied to many fermented foods.
Description
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Appendix 5b:
Nor-Khalzura, M-A-R., Flint, S.H., McCarthy, O.J., Palmer, J.S., Colding, M., Jaworska, A. (2012)
Development of made-in-transit set culture yoghurt: effect of increasing the concentration of
reconstituted skim milk as the milk base, International Journal of Food, Science and Technology,
47, 579-584
Keywords
Made-in-transit (MIT) manufacture, Food supply, Yoghurt manufacture, Food distribution