Doctoral Degrees (Food Science)

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Browsing Doctoral Degrees (Food Science) by Subject "Active Modified atmosphere packaging (active-MAP)"

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    Modelling and optimization of active modified atmosphere packaging for pomegranate arils
    (Stellenbosch : Stellenbosch University, 2017-12) Belay, Zinash Assefa; Opara, U. L.; Caleb, Oluwafemi James; Mahajan, P. V.; Sigge, G. O.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Active modified atmosphere packaging (active-MAP) is a well-proven postharvest technology used to preserve the quality and extend the storage and shelf life of fresh fruit under optimally designed conditions. Successful active-MAP design can be achieved by the mathematical integration of produce physiological characteristics, packaging material properties, and equilibrium gas mixture suitable for the product. The mechanisms by which active-MAP influences fruit quality involve physiological and enzymatic reactions that can be accelerated or reduced depending on the environmental conditions during storage. Therefore, understanding the experimental design and fundamental physiological processes occurring during storage condition are important in the development of an optimal produce-specific active-MAP. Low O2 limit for pomegranate arils was identified at 5 and 10 °C and the responses were monitored using real time respiration rate (RR), respiratory quotient (RQ), emission of volatile organic compounds (VOCs) and microbial growth. The results showed that pomegranate arils could tolerate down to 2.18% O2 during storage at 5 °C and 2.28% O2 at 10 °C. These findings highlighted the importance of selecting appropriate MAP materials with desired permeability to alleviate rapid depletion of O2 and excessive accumulation of CO2 at 10 °C inside the package. The impact of active-MA on quality attributes of ‘Wonderful’ pomegranate arils were investigated at cold (5 °C, 95 ± 2% RH) and ambient storage (20 °C, 65 ± 2% RH) conditions. Low O2 (5-10%) atmospheres significantly maintained antioxidant properties of arils, whereas significantly lower aerobic mesophilic bacteria, yeast and mould counts were found at super-atmospheric O2 (70%). Storing pomegranate arils under ambient condition resulted in quality deterioration and short shelf life. The effects of low O2 and super-atmospheric O2 on RR of ‘Wonderful’ pomegranate arils were analysed at 5 °C. Michaelis-Menten (MM) enzyme kinetic models were applied to determine the inhibition effects of CO2 concentration on O2 consumption rate. The results showed that both storage atmosphere and temperature had significant effects on aril RR. The MM competitive inhibition model best described the effect of CO2 on O2 consumption rate at low O2 and super-atmospheric O2 (R2 > 99%). The findings showed that super-atmospheric O2 had no effect to retard the metabolic process. A simplex lattice mixture design (SLMD) approach was applied to optimize gas composition for storing arils, and effects of temperature on the optimum gas was studied. A special cubical model were developed for the responses (RR, RQ, ethylene production rate and microbial quality) and the coefficients of model parameter estimates (β1, β2, β3, β12, β13, β23 and β123) and ternary contour plots were characterised. The predicted optimium gas mixture (O2:CO2) was 2% O2:18% CO2); and at this atmosphere, the minimum values of RR were 0.26 mL O2 kg-1 h-1 and 0.78 mL CO2 kg-1 h-1, while ethylene production rate was below the detection limit. Under these conditions, the growth of aerobic mesophilic bacteria (3.9 log CFU mL-1), yeast (3.8 log CFU mL-1) and mould (2.3 log CFU mL-1) were quantified. Increasing the storage temperature by 10 °C resulted in a threefold increase in aril RR. Using the same SLMD approach, the optimum gas composition required to maintain individual quality attributes was predicted. Variation in optimal gas mixture for individual quality attributes of arils were observed. According to the model parameter estimates, the optimum gas composition (O2:CO2) was established (6-7% O2:7-8% CO2) for individual sugars, organic acids, antioxidants and colour attributes. The optimum gas composition to maintain aril hardness and volatile compounds (monoterpene and ketones) was 2% O2 and 18% CO2. On the other hand, the optimum atmosphere for aldehydes was 2% O2 and 2% CO2. An integrated designing approach was applied to configure a packaging system for arils capable of modifying atmosphere and in-package relative humidity by designing modified atmosphere humidity package (MAHP) system. Cellulose based NatureFlex® (NF) film, bi-axial oriented polypropylene (BOPP) (PF) film and combinations of the two films were used. The 100% NF package created the lowest in-package RH (60-66%) and the highest reduction of O2, which resulted in arils dryness during storage. The 100% BOPP film resulted in saturated RH and in-package water vapour condensation. The optimized package design using 66% PF and 33% NF films best maintained the overall quality of pomegranate arils. This study demonstrated the potential of SLMD as an innovative tool to optimize the gas composition and improve packaging design for effective cold storage of minimally-processed fresh produce such as pomegranate arils. The results obtained also provide new information on the optimum condition required to maintain specific quality parameters for the commercialization of active-MA for packaging and marketing of pomegranate arils.