Effect of Calcium Chloride and Hydrocooling on Postharvest Quality of Selected Vegetables

Precooling and postharvest application of calcium chloride (CaCl2) on produce has positive effects in maintaining the produce quality during storage. However, there is variation in the response of the produce to different CaCl2 concentrations. As a result, there is need to establish optimal concentrations of calcium chloride that can extend postharvest life of targeted produce. Fresh good quality produce (tomatoes, carrots, courgettes and African eggplants) of uniform size and maturity were harvested and sampled into four portions. One was a control, hydrocooled with water only at 2±1 C and the others were hydrocooled with water containing CaCl2 at 0.5%, 1.0% and 1.5%. After hydrocooling, tomatoes, African eggplants and courgettes were stored at 10 C, while carrots were stored at 7 C, all at 95% constant relative humidity, and sampled every two days for quality assessment. Weight loss, chilling injury, vitamin c and β-carotene loss were reduced by application of calcium chloride. Titratable acidity decrease and increase in total soluble solids and specific sugars was also slowed by application of CaCl2.


Introduction
Horticultural produce have contributed significantly to Kenya's economy, attracting good returns thus leading to increased production (Muthoka & Ogutu, 2014).However, to maximize profits from the increased production, which is usually accompanied by huge postharvest losses, there is need to develop proper postharvest handling practices (Dhillon & Kaur, 2013).This includes precooling of produce to eliminate the field heat and respiratory heat, thus delaying deterioration (Senthilkumar et al., 2015).Surface treatment of produce has been shown to delay physiological decay and stabilize surface of produce, thus delay overall degradation (Akhtar et al., 2010).Hydrocooling of fresh produce is designed to precool the produce, remove soil, pesticide residues and microbes that cause quality loss.In addition, hydrocooling aids in removal of cell exudates that may further support microbial growth in the perishable produce (Gil et al., 2009).
Various sanitizers have been used in the past in hydrocooling and packing operations.Chlorine in water has been used during hydro-cooling and in disinfection of pack house, packaging and transport facilities.Hydrogen peroxide (food grade) has also been used as a disinfectant at concentrations of 0.5% or less, and is effective in inhibiting development of postharvest decay caused by a number of fungi (Acedo, 2010).Although there are many sanitizers available, the cost of acquisition and their suitability for application in the food industry poses a challenge on their use.Other substances used include Organic and inorganic salts which must be of the Generally Regarded as Safe category(GRAS) (Youssef et al., 2012).
Calcium chloride has been used previously on various produce including apples, mangoes, loquat and strawberries (Souza et al., 1999;Akhtar et al., 2010;Hussain et al., 2012;Dhillon & Kaur, 2013b), showing positive results in maintaining postharvest quality of the produce.nutrition and economy.In the current study, tomatoes were selected based on the economic importance of tomato value chain in the country (ERA-MOALF 2015), while carrots and courgettes were selected due to their production levels and potential for income generation (ERA-MOALF 2010).African eggplant, a traditionally important vegetable was studied in this context as there is little information on their postharvest management practices (Kitinoja et al., 2011;Msogoya et al., 2014).
This study was undertaken with the objective of establishing the optimum concentration of calcium chloride to be applied on the selected produce and also evaluate the effect of these concentrations on microbial quality of produce.

Materials and Methods
The produce were harvested at their commercial maturities, characteristic for each product, and sorted for uniformity in size and stage of maturity, and also to eliminate the injured, diseased and deformed produce before proceeding with the experiment.

Hydrocooling of Selected Perishables
Upon harvest, the experiment was laid out in the laboratory in a completely randomized design.Produce hydrocooling was done using a shower type hydrocooling system with chilled water as described by (Chepngeno et al., 2015).In this study, the chilled water (2±1 0 C) contained CaCl 2 at 0 % w/w, 0.5 % w/w, 1.0 % w/w and 1.5 % w/w.Storage was done at 10 0 C for 15 days in tomatoes, courgettes and African eggplants at 10 0 C and carrots at 7 0 C, for 9 days.Physical, chemical and microbiological assessments were then done at two days interval.

i. Weight loss
Weight loss in fruits was measured gravimetrically on individual fruits as described by (Juan et al., 2007), where individual fruits were placed in trays, kept at respective temperature regimes with a constant relative humidity of 95% and weights of five fruits per treatment taken at intervals of two days.The percentage weight loss in the fruits was determined as a function of the original sample weight using the equation below: ii. Colour Produce external colour was evaluated objectively using a Chroma colour meter (CR-300, Minolta Japan) (Hernandez-Munoz et al., 2008).Four readings were taken from each fruit at 90 0 interval using five fruits from each treatment and measurements done in triplicate.CIELAB output readings were obtained and used to obtain the Hue angle, as shown.

= * *
(2) iii.Decay Incidence/ spoilage/ Chilling injury The storage rot or chilling injury incidence from produce subjected to the treatments was determined as the percentage (count) of the sample with decay from total proportion.

i. Respiration rates
Respiration rate measurement was done by taking produce of known weight in jars of known volume whose covers were fitted with a self -sealing rubber septum for gas sampling and incubated at room temperature for one hour.Headspace gas was drawn using airtight syringe and injected into the gas chromatograms (Model GC-8A Shimadzu Corp., Kyoto, Japan) fitted with thermal conductivity detector.Rate of carbon dioxide production was calculated as mg CO 2 /Kg/hr at standard atmospheric pressure.

i. Beta carotene
Beta carotene content was analyzed using open column chromatography and UV spectrophotometer.Extraction was done using acetone and petroleum ether as described by (Delia B Rodriguez-Amaya & Kimura, 2004).The extract was then evaporated to dryness at 40 0 C on a rotary vacuum evaporator (RE 100 BIBY with a water bath).
The residue was dissolved in petroleum ether and the sample introduced into the chromatographic column packed with silica, and eluted with petroleum ether.Absorbance was read at 440 nm in a UV-Vis spectrophotometer (Shimadzu model UV -1601 PC, Kyoto, Japan).Beta carotene content was then calculated using a freshly prepared beta carotene standard calibration curve.
ii.Total soluble solids (TSS) and titratable acidity (TTA) The total soluble solid (TSS) content was determined using a digital refractometer (Model PAL-S, Atago, Tokyo, Japan) and expressed as degrees brix (°B).Total titratable acidity was determined by titrating a known volume of the juice against 0.1N sodium hydroxide with phenolphthalein indicator.

iii. Specific Soluble sugar content determination
Soluble sugar content (glucose, fructose and sucrose) was determined using the method described by (Sánchez-Mata et al., 2002), with a few modifications where 10 g of the solid sample was weighed and homogenized before being transferred quantitatively to a conical flask.50 ml of 96% alcohol was added and refluxed at 100 0 C for 1 hour.The samples were then stirred and the slurry filtered.This was then evaporated in a rotary evaporator at 60 0 C to dryness, and then 10ml of distilled water was added to the dried sample and shaken to dissolve the extract.From the solution, 2 ml of the sample was drawn and 8 ml of acetonitrile added.
The solution was then filtered using membrane filter.The sample was then injected into the HPLC with NH2P-50E column 10 Pkm pressure and 1ml/min flow rate and Refractive index detector and the quantity of specific sugars determined using freshly prepared standard sugar concentration curve.

iv. Vitamin C
Vitamin C was determined using the method described by (Mamun et al., 2012) with a few modifications.About 10 g of sample was weighed and extracted with 0.8% metaphosphoric acid.This was made to 20 mL of juice.
The juice was centrifuged at 10000 rpm (Kokusan H-200 Tokyo Japan), at 4 0 C for 15 minutes.The supernatant was filtered and diluted with 10 mL of 0.8% metaphosphoric acid.This was passed through 0.45 µ filter and 20 µL injected into the HPLC machine.HPLC analysis was done using C18-4D column and Shimadzu UV-VIS detector.The mobile phase was 0.8% metaphosphoric acid, at 1.2 mL/min flow rate and wavelength of 266.0 nm.

i. Total plate count
Fruits of known weight from treatments above were washed in sterile distilled water using a shaker, with fruit to distilled water ratio as 1:9.The wash water was then further diluted using peptone water, up to 10 5 and plated in triplicate on total plate count agar prepared as per manufacturer's instructions and incubated at 25 0 C for 24 hours (Monaghan et al., 2009).

ii. Total yeast and mould
Fruits of known weight from treatments above were washed in sterile distilled water using a shaker, with fruit to distilled water ratio as 1:9.The wash water was then further diluted using peptone water, up to 10 5 and plated in triplicate on potato dextrose agar prepared as per manufacturer's instructions and incubated at 25 0 C for 24 hours (Badosa et al., 2008).

Data Analysis
Data obtained from the experiment was analyzed for variance (ANOVA) using Genstat discovery edition 4, in a randomized complete block design (RCBD) in replicates so as to establish the effect of calcium chloride concentrations and also the storage time in days on the measured parameters.

Weight Loss
Weight loss in all the produce hydrocooled with the calcium chloride solutions at 0%, 0.5%, 1.0% and 1.5% increased gradually over the storage time regardless of the treatment as shown in influenced by both the storage time and the CaCl 2 concentration used.The difference between the various CaCl 2 concentrations was significantly different (P≤0.05).The produce responded differently to the calcium chloride solutions.Tomatoes hydrocooled with water containing 1% CaCl 2 showed the least weight loss, attaining 1.30% loss in day 9, which was remarkably the lowest, for all treatments.Carrots showed higher weight losses when hydrocooled with water containing CaCl 2, attaining 9.9% weight loss at 0.5% CaCl 2 with the control, water only (0% CaCl 2 ) only attained a weight loss if 9.0%.Courgettes showed decreasing weight loss with increasing CaCl 2, concentration.The least weight loss was obtained in the 1.5% CaCl 2, with 4.42% in day 9 as compared to 0% CaCl 2 whose weight loss was 8%.African eggplants showed less percentage weight loss at 1% CaCl 2, with 4.75 %.This was significantly lower than in fruits hydrocooled with water only.Increasing CaCl 2 concentration to 1.5% resulted in higher weight loss again, reaching 6.04 % on day 9.The occurrence of higher weight loss at higher salt concentrations is attributed to existence of difference in water potential during hydrocooling.Similar findings were found in tamarillo fruits treated with various CaCl 2 concentration deeps by Pinzón-Gómez et al., (2014).
Figure 1.Percentage weight loss in vegetables when hydrocooled with water containing calcium chloride.Percentage weight loss in vegetables was calculated as a function of the initial weight.5 fruits were monitored throughout the study period.Data is presented as means ±SE.Calcium chloride concentrations in the hydrocooling water was 0% (HCCR), 0.5%, 1.0% and 1.5%

Respiration Rates
Respiration rates in produce were influenced by both the calcium chloride content in water and storage time.A significant difference (P≤0.05) was observed between 0%, 0.5%, 1.0% and 1.5% CaCl 2. Effect of the various concentrations of CaCl 2 on produce respiration is as shown in Tomatoes treated with 1% CaCl 2 showed lower rates of respiration, throughout the storage period.In courgettes and African eggplants, the least respiration rates were observed in 1.5% CaCl 2. Carrots showed no positive response with addition of calcium chloride; instead the respiration rates increased with increasing calcium chloride concentration.
Calcium is associated with ripening in fruits and sufficient amounts have been shown to reduce transpiration rates and consequently the respiration rates.High levels of calcium in cell walls have also been found to reduce activity of fruit softening enzymes (Pinzón-Gómez et al., 2014).

Tomatoes Eggplants
Carrots Courgettes Figure 2. The Respiration rates in vegetables during storage.Data is presented as means ±SE.Calcium chloride concentrations in the hydrocooling water was 0% (HCCR), 0.5%, 1.0% and 1.5%

Titratable Acidity
Titratable acidity in all the produce declined over the storage period as shown in Figure 3.In tomatoes, %TTA declined from 0.6 % to range between 0.4 % and 0.28% after 9 days.The least titratable acidity loss during storage of produce occurred in tomatoes at 1% CaCl 2 , attaining 0.4% TTA.Courgettes and African eggplants showed the least decline in acidity at 1.5% CaCl 2 concentration in the hydrocooling water, declining from 0.05% to 0.04 % and 0.03% to 0.01% respectively.Carrots had the highest decline in acidity at 1.5% CaCl 2 .
Interaction between storage time and CaCl 2 concentration applied was observed.These were significantly different (P≤ 0.05).A negative correlation was observed between TSS and TTA in the produce.Since CaCl 2 was observed to lower respiration rates, it therefore resulted in reduced rate of utilization of organic acids as substrate for respiration in the produce and delayed ripening of tomatoes Mahajan and Dhatt (2004).These correlation has previously been seen in tomatoes and mangoes (Rathore et al., 2007;Senevirathna & Daundasekera, 2010 ).

Total Soluble Solids
The change in soluble solid content in the produce during the study period is shown in Figure 4.By the end of the storage period, TSS in CaCl 2 treated samples was lower than the control (water only) in tomatoes, courgettes and eggplants, although at differing concentrations.In tomatoes, the least TSS of 2.6% on day 9 was recorded in produce hydrocooled with 1.0% CaCl 2. Courgettes and African eggplants had the least TSS in 1.5% CaCl 2 treated samples with 4.7% and 6.4% respectively.Carrots had the least TSS in 0% CaCl 2 on day 9; with TSS increasing with increasing CaCl 2 concentrations in the water.
The increase in TSS during storage is attributed to the breakdown of starch into sugars or the hydrolysis of cell wall polysaccharides during ripening in climacteric fruits i.e. the tomatoes (Azene et al., 2014 andYoussef et al., 2012) and bananas (Khanbarad et al., 2012).However, the increase in TSS that occurs in non-climacteric produce may be associated with water loss (Hailu et al., 2008), or increased metabolic reactions due to invasion by microbes or chilling injury (Khanbarad et al., 2012).The lower TSS with pre-cooling could be due to slowing down of metabolic activities.The slower rate of TSS increase in produce hydrocooled and kept at low temperature is due to the effect of precooling which reduced field heat from fruits, restricting respiratory activities and inhibited water loss.A similar phenomenon was reported by Makwana et al. (2014) when mangoes were hydrocooled using water at 8 0 C for eight hours and stored at 8 0 C.In the carrots, courgettes and African eggplants which are non-climacteric commodities, TSS build-up during storage is due to the produce weight loss, resulting from moisture loss.Positive correlation between weight loss and TSS similarly observed in this study has been reported by Hailu et al. (2008) in stored carrots and in strawberries by Hernandez-Munoz et al. (2008).

Tomatoes Eggplants Carrots Courgettes
Figure 4. Total soluble solid content as influenced by various CaCl 2 concentrations during storage.Data is presented as means ±SE.Calcium chloride concentrations in the hydrocooling water was 0% (HCCR), 0.5%, 1.0% and 1.5%.

Specific Sugar Composition
The change in specific sugar composition in all the produce was significantly (P≤ 0.05) affected by the storage time.Longer storage time resulted in greater deviation in the sugar composition from those of fresh samples.As shown below in Figure 5, glucose and fructose increased during storage in all produce, while sucrose declined.

Glucose Fructose Sucrose
Figure 5. Specific sugar composition in vegetables during storage.Data is presented as means ±SE.Calcium chloride concentrations in the hydrocooling water was 0% (HCCR), 0.5%, 1.0% and 1.5%  In the CaCl 2 treatments, glucose and fructose increased in all produce during the storage period.At the start of the experiment, tomatoes had initial sugar content at 0.55 mg/100g, 0.38 mg/100g and 0.80 mg/100g for glucose, fructose and sucrose respectively.This increased to 1.44 mg/100g and 1.1 mg/100g in glucose and fructose under 1.5% CaCl 2 treatment.The least changes in sugar composition occurred at 1% CaCl 2 in tomatoes .This was significantly different (P≤ 0.05) from the control and 1.5% CaCl 2 .Similar trends were observed for African eggplant, courgettes and carrots with least change in sugar content at 1.5% CaCl 2 in courgettes and African eggplants, being significantly different (P≤0.05) from control while carrots responded best to 0% CaCl 2 .
The existing positive correlation observed between respiration rates, weight loss and soluble solid contents was similar to the findings of Irfan et al., (2013) in fig fruits.This shows that CaCl 2 treatment can be used in maintenance of postharvest quality.Similar correlations have been observed in strawberries by Chen et al. (2011) with CaCl 2 concentrations.He attributed the higher specific sugar change in produce at higher CaCl 2 to existence of phytotoxicity (Pinzón-Gómez et al., 2014).

Beta-carotene
Beta carotene in produce under study was significantly affected by storage time and concentration of CaCl 2 applied.The produce response to treatments is as shown in Figure 6.In carrots, courgettes and African eggplants, Beta carotene content decreased gradually during storage for all treatments.β-carotene in carrots declined from 3.93 mg/100g to 3.13, mg/100g in the control in day 9.It also declined to 3.12 mg/100g, 3.21 mg/100g and 3.08 mg/100g for 0.5%, 1.0% and 1.5% CaCl 2 respectively.
This increase in beta carotene can be attributed to the unmasking of the carotenoids following chlorophyll degradation during ripening of tomatoes.Similar findings have been observed in produce such as mangoes and passion fruits (Makwana et al., 2014;Yumbya et al., 2014).
Effects of CaCl 2 on beta carotene followed the trend in titratable acidity.This was however not statistically different from the samples hydrocooled with portable water only during the period of this study.These findings are similar to those of (Negi & Roy, 2000) who found that longer storage time resulted in higher loss of beta carotene content accompanied by progression of senescence (Msogoya et al., 2014).

Vitamin C
The ascorbic acid quantity in the produce was significantly affected by storage time and precooling treatment.A decline in ascorbic acid was observed in all produce under study in all treatments as shown below in Figure 7.

Tomatoes African Eggplant
Carrots Courgettes Figure 7. Vitamin C content in produce treated with CaCl 2 during storage.Data is presented as means ±SE.Calcium chloride concentrations in the hydrocooling water was 0% (HCCR), 0.5%, 1.0% and 1.5% Use of calcium chloride in the hydrocooling water resulted in slower rate of loss of Vitamin C in courgettes and eggplants both at 1.5% (w/v) and tomatoes at 1 % w/v.In carrots, no positive effect was obtained at all the concentrations tested.The change was however significantly high at 1.5% CaCl 2 , implying that the osmotic pressure existing between the wash water and the internal carrot composition may have resulted in higher oxidation of ascorbic acid, utilized in respiration together with other organic acids present.
Vitamin C retention was highest in carrots hydrocooled with 1.0 % CaCl 2 declining from 5.6 mg/100 g to 4.36 mg/100 g on day 9.This was however not significantly different (P≤0.05) from those hydrocooled with pure water with 0.5% CaCl 2 , both kept at 7 0 C.
In tomatoes, the Vitamin C content declined from 21.63 mg/100g at the start of the experiment, reaching the lowest of 16.53 mg/100g in in 1.5% CaCl 2 by the 9 th day.Similar findings were observed by (Moneruzzaman et al., 2008) in tomatoes, where decline was observed during ripening of tomatoes.
Eggplants had an initial vitamin C content of 7.3 mg/100 g which declined under the control experiment to 3.6 mg/100g by the 9 th day.Although this was lower than the findings of (Eze & Kanu, 2014), who reported vitamin C content of 14mg/100g, in African eggplants, Msogoya et al., (2014) observed similar trends for fruits under the control, where at harvest; vitamin C was at 8.08 mg/100g which declined to 4.84 mg/100g upon storage.The difference here could be due harvesting stages Eze and Kanu (2014) used unripe fruits while Msogoya et al., (2014) termed fruits used as at harvesting stage 2.
Ascorbic acid is a highly sensitive nutrient, commonly used as a quality indicator (Babu et al., 2015).The decline in vitamin C has been observed in other vegetables such as broccoli Carvalho and Clemente (2004), capsicum Rahman et al. (2015) and in tomatoes (Žnidarčič & Požrl, 2006).The decrease is due to natural degradation Carvalho and Clemente (2004) a product of oxidation and enzyme catalysts activity present in the fruits (Žnidarčič & Požrl, 2006).

Colour
Hue angles in the produce also declined over the storage time as shown in Figure 8. Hue angles in tomatoes declined by 15.2%, 12.33 %, 10.2% and 14.4% for 0%, 0.5%, 1.0% and 1.5% CaCl 2 respectively in tomatoes by the end of the 9 day study period.
A significant decline in L* values was observed in the African eggplant fruits.The decline ranged between 10.7% for 0% and 3.1% for 1% CaCl 2 .The declined appeared to accompany development of surface lesions in the produce which was attributed to chilling injury in the produce.Although a change in hue angles was also observed to decline, it followed the severity of skin lesions.The decline was between 14.7% and 6.8% for 0% and 1% CaCl 2 respectively.These were significantly different (P≤0.05).
Courgettes on the other hand showed no significant change (P ≤0.05) in hue angle during storage, with change only occurring in the L* values over storage time.L* values declined progressively during storage, with the greatest decline occurring in 0.5% treatment with 3.03%.This was not statistically different (P ≤0.05) from control and those of 1% and 1.5% CaCl 2 respectively.Similar findings were observed by Apai et al. (2007) on the peel of longan fruits; Tripathi et al. (2013) in apple fruits and Senevirathna and Daundasekera (2010) reported that 4% CaCl 2 had delayed colour development in tomato fruits although it was not significantly different from those of untreated fruits.These results further underscore the findings in this study where 1.0 % CaCl 2 showed the least colour change at the end of the storage period.
Calcium chloride has been shown to have an effect in ethylene production, where it suppresses its synthesis Ishaq et al. (2009), thereby delaying its role in unmasking the yellow and red carotenoids in climacteric fruits such as tomatoes (Pinzón-Gómez et al., 2014).This could possibly explain the cause of reduced colour change in tomatoes.
Figure 8. Hue angle changes in vegetables during storage.5 fruits were monitored throughout the study period Data is presented as means ±SE.Calcium chloride concentrations in the hydrocooling water was 0% (HCCR), 0.5%, 1.0% and 1.5%

Decay Incidence
The decay incidence in all the vegetables increased gradually in all produce as shown in Figure 9 the optimum levels to delay this deteriorations in the concentrations studied were 1.0%, 1.5 %, 0% and 1.5% for tomatoes, eggplants, carrots and courgettes respectively Application of calcium chloride delayed the onset of deterioration in all produce, by between 3 to 7 days, although the products responded optimally to different concentrations.
The percentage deterioration due to shriveling of fruits ranged between 19.3% and 33 % in tomatoes, with 0% CaCl 2 at 32.8% while 1.0% CaCl 2 was 19.3% after 15 days of storage African eggplants deterioration characterized by development of surface lesions and browning around the seeds ranged between 26.7% when hydrocooled with water containing 1.5% CaCl 2 and 48.7% at 0% CaCl 2 , at 9 days after storage.Carrots at the end of 9 day storage period, the proportion of deteriorated produce due to re-sprouting and development of dark coloration at the tips was between 7.4% at 0 % CaCl 2 and 14.3% at 1.0% CaCl 2. Deterioration in courgettes characterized by surface pitting and development of pinched ends ranged between 22.0% in 1.5% CaCl 2 and 26.3 % at 0.0% CaCl 2.
Produce spoilage and deterioration is a function of degradation of the cell wall (Franco et al., 2006).Application of a substance that delays any form of cell disintegration has been found to extend the postharvest life of produce.Calcium chloride has previously been reported to delay onset of deterioration in pear fruits (Sugar & Basile, 2011).This is attributed to calcium's interaction with the cell walls components resulting in maintenance of the cell integrity, Akhtar et al. (2010) for a long period of time (Babu et al., 2015) thus resulting in improved postharvest life.Calcium ions have been observed to form bridges with peptic molecules of the middle lamella.As a result, better cell cohesion is maintained leading to better PH quality of produce (Franco et al., 2006).

Microbial Load
The microbial quality of the fresh produce varied significantly between the produce.Carrots had the highest microbial population both for yeast and mold and in total plate count.Hydrocooling the produce generally reduced the initial microbial loads, although it did not completely eliminate the microbes from the produce.The hydrocooling of the produce with various concentrations of CaCl 2 yielded results with significant difference at (P≤ 0.05).Microbial populations generally increased over the storage period as shown below in Figure 10 for TPC and Figure 11 for yeast and molds.After washing, TPC together with the yeast and mold increased over storage time, although the increase was slow and gradual.The slow growth in population can be attributed to the low storage temperatures of produce.Least microbial growth in all produce occurred in 1.5% CaCl 2 .
2.5 2.7 2.9 This can be attributed to osmolysis occurring in produce due to high salt concentration.Microbial infestation often leads to decay, becoming a major cause of food spoilage (Artés & Gómez, 2006).Abadias et al. (2008) indicated that it is almost impossible to eliminate microbes from fresh vegetables completely because the concentrations required to achieve this may be harmful to the product or consumer.However, upon storage, microbial populations increased on the surface of the produce regardless of the pretreatment applied.The microbes showed a typical logarithmic increase, which can be attributed to cell multiplication.Similar findings of high microbial loads have previously been reported in carrots in Spain by Abadias et al. (2008) when freshly cut and whole fruits and vegetables were sampled.
Due to their versatile nature, microbes grow on several surfaces, exhibiting different characteristics.However, low temperatures in which the fresh produce are kept have been shown to delay or retard their growth, thus delaying the overall quality deterioration as they limit the number of pathogens that can grow on the substrate (Pla et al., 2008).

Conclusion
Calcium chloride addition to the hydrocooling water in this study showed varying responses in the selected vegetables.The highest concentration of 1.5% CaCl 2 resulted in less decay and a lower microbial population in all samples.However, the specific effect of the salt concentration on weight loss, vitamin C retention, beta carotene content, total soluble solids and titratable acidity was specific to each product.
By considering the above effects, 1.0 % CaCl 2 was the best concentration in this study for tomatoes, resulting in optimum characteristics studied throughout the study period.
For courgettes, the best concentration was at 1.5% while carrots exhibited the best postharvest quality characteristics when hydrocooled using cold water without calcium chloride application.
Application of CaCl 2 at the different concentrations delayed the onset and development of chilling injury symptoms in African eggplants.However, the concentrations used in this study only delayed and reduced the

Figure 2 .
Addition of calcium chloride to the hydrocooling water significantly reduced respiration rates (P≤0.05) in tomatoes, African eggplants and in mg/kg/hr Storage time in Days courgettes, while increasing respiration rates in carrots.