[4-1015-A] Postharvest/Food Technology and Process Engineering (1)

[4-1015-A-03] Effect of High Voltage Electric Field on the Shelf Life of Mini Tomato Fruits

*RAMNESH RAMNEEL KISHORE¹, Daisuke Hamanaka¹ (1. Kagoshima University(Japan))

Keywords:High voltage electric field, climacteric fruits, respiration rate, Tomato

High voltage electric field (HVEF) which is a non thermal food preservation technique that processes food without leaving any chemical residues and radiation is one of the emerging and a new area of research in the field of food preservation. Recent research indicates the use of HVEF on agricultural commodities reduces respiration rates of climacteric fruits, inhibit enzymatic and microbial activity which leads to extending the shelf life of fruits and vegetables. A major advantage of using high voltage food preservation technique is that it consumes low energy and prohibits the use of any chemical preservatives. The main objective of this research is to investigate the effects of HVEF on the shelf extension of mini tomato fruits. Monitoring of physiological responses and quality evaluation were performed during the storage test period of 3 weeks. The mini tomato fruit samples were obtained from a local distributor in Kagoshima and the samples were carefully graded for optimum quality to be used in this experiment. The total duration of sample analysis was 3 weeks (21 days). In the first two weeks the samples were treated to continuous electric field treatment; this was the test to study continuous effect of electric field on sample quality. On the 3rd week; the electric field was shut off and samples were analyzed for further 1 week to test the shelf life storage stability of tomato fruits post EF treatment. For EF and control treatment the total frequency of monitoring or analysis was 7 times; which is a representation of different number of day intervals over the 2 weeks period. For shelf life storage testing period the samples were analyzed over a period of 1 week. Two distinctive type of EF setup was used to study the quality attributes and respiration rate respectively. For measurement of quality attributes, the samples were placed inside a large electric field incubator (High voltage 7kV A/C- power supply (N- TeFe II) at 60Hz) for EF treatment and for control experiment another similar type incubator was used but without EF treatment. The treatment temperature was 1⁰C and relative humidity was approximately 95%. The quality attributes evaluated in this study were PLM (Physiological loss of mass), TSS (total soluble solid), Brix, hardness and color properties. For respiration rate measurement (CO₂) production, 2kV aluminum parallel plate configuration electric field setup was used. The HVEF system consisted of a power source with an output voltage of 2kV (NF Corporation Japan, Model: EC750SA) with A/C- power supply (sine waveform) at a frequency of 60Hz. The samples were placed into acrylic desiccator and sealed off with an air tight lid. One end of the desiccator was connected to the air pump via flexible tube while the other end was connected to much smaller desiccator that housed the CO₂ sensor. For control, similar setup was used but without EF plates in the desiccator. The entire system was setup inside the incubator with controlled temperature and RH. Four incubators with EF setup were used, each with a corresponding temperature of 0, 1, 3, 5⁰C respectively. The CO₂ production of the fruits were assessed at 10 minute intervals for 2 hours. For post EF treatment analysis, the samples were transferred inside perforated bag with gas septum attached and the bags were sealed and further stored for 1 week to study shelf life stability. The gas concentration was analyzed using a gas chromatography machine. The experiments were performed in triplicates. Analysis of the PLM indicated that in the two weeks of continuous treatment, the electric field treated samples had suppressed weight loss on D1, D2 and D3 respectively, whereas for D7 and D10 samples; the control treatment showed more reduction in weight loss. During shelf life storage period, the PLM of EF samples was significantly lower than the control treatment. On day 7, maximum weight loss was seen, however the weight loss of EF sample was still lower compared to control 0.60 and 0.87% respectively. The total soluble solid content of HVEF treated samples were higher in concentration compared to the control in the 2 weeks of continuous treatment. Post EF treatment, the EF samples still constituted to higher Brix content overall. On the day 7 of shelf life storage the average TSS content between EF and control sample were 7.06 and 6.52 Brix respectively. The fruit firmness during 2 weeks of continuous treatment indicated that on day 4 and 7, the EF samples were a lot slightly firmer with 0.84N and 0.83N difference between EF and control sample respectively. Post EF treatment, the EF treated sample were consistently firmer throughout the 1 week storage period with an average hardness of 6.7N for EF sample and 6.5N for control.