A Comparative Study on the Interaction Effect of Date of Planting, Variety and Head Diameter on the Post Harvest Quality of Broccoli Stored in Refrigerated Condition

Broccoli (Brassica oleracea L.var.italica plecnk.) is also known as calabrese or green sprouting broccoli, Italian broccoli, asparagus broccoli, belongs to family Brassicaceae, a cool season crop and closely related to cauliflower. Broccoli is an important vegetable and a new introduction to India. It is cherished for its delicious taste, flavour and nutritive value. The crop is annual and grows to maturity in about 75 to 95 days, depending on cultivar, season and planting date. Though it is grown abundantly in the foothills of the Himalayas, in the terai regions of West Bengal, now-a-days it is gaining popularity among the vegetable growers in the Gangetic plains of West Bengal mainly due to its rich nutritional values but the information on post harvest technology aspect of the crops suitable for this region is scanty (Cantwell and Suslow, 1999).
       
Taking into consideration the short shelf life, high perishability and short period of availability of broccoli, the current work was undertaken to overcome the problems cited.

Two varieties of broccoli were grown in the Horticultural Research Station, Mondouri, West Bengal at different date of sowing heads and harvested after two months in the beginning of the year 2015 at different head diameters as stated below and they were brought to the laboratory immediately in plastic crates and cooled by room condition for 3 hours. Then they were trimmed and packed in polypropylene bag and stored in as well as refrigerated condition (5±1°C).

 
Observations recorded
 
Physiological loss in weight (%), yellowing (%), TSS (°B), Chlorophyll (µg/g), ascorbic acid (mg/100 g) were estimated  during the period of storage by following standard procedures as described under physico chemical analysis in refrigerated condition (5 days interval).
 
Physical and chemical analysis
 
Physiological loss in weight (PLW)
 
PLW was calculated as total weight loss %, based on the initial weight (before storage) and weight loss at the day of sampling during storage (Nath et al., 2011).  
Ascorbic acid
 
Volumetric method of ascorbic acid determination (2,6- Dichlorophenol-Indophenol Visual Titration Method) was done using 2, 6-dichlorophenol indophenols which gets reduced to a colourlessleuco-base by ascorbic acid and the ascorbic acid gets oxidised to dehydroascorbic acid. Though the dye is a blue coloured compound, the end point is the appearance of pink colour. The dye is pink coloured in acid medium (Ranganna, 1986).
   Chlorophyll
 
Total chlorophyll content was determined by spectrophotometric method (A.O.A.C,1990). A known amount of tissue sample by weight is taken and chlorophyll is extracted in 80% acetone until the residue has no more green colour. The filtrate or supernatant is made upto known volume with 80% acetone and the Optical Density (OD) value is then measured through 660 nm and 642.5 nm wavelength in a colorimeter against blank. Using the adsorption coefficients, the amount of chlorophyll is calculated as follows:


 
Total soluble solids (TSS) °Brix
 
TSS was determined by Hand Refractometer (Erma Hand Refractrometer I.S.O 2173), by principle of total reflection which was calibrated at 0°B is checked before use by placing few drops of distilled water on the prism in the specimen chamber of the refractrometer. The refractive index is the ratio of the speed of light in vacuum to its speed in a substance and is used as a measure of concentration of solutes in solution (Peris, 2004).
 
Yellowing percentage
 
Whole green broccoli head is divided into four parts out of 100 per cent. The area which becomes yellow is recorded visually according to the four parts divided. There were two conditions of yellowing, one where there was gradual yellowing while the other was with the patchy development of colour.
 
Marketability (%)
 
The marketability of broccoli was determined on the basis of colour, texture or crispiness, flavour and defects like yellowing, browning and decay and expressed in percentage (%). Upto an amount of 50% was considered to be marketable.
 
 

Physiological loss in weight (PLW) %
 
PLW increased with the advance of storage days in Table 1. Higher loss in weight was observed in late sown crop (D₃) increasing from 2.17 to 6.69% throughout the storage period while the lowest loss in weight was noted in early sown crop (D₁) while minimum loss in weight was prominent in Aishwarya (V₁) ranging from 1.43 to 5.08% from 5 to 15 days after storage.


       
From the statistically analysed data in Table 1, the least value of loss in weight throughout the storage was observed in small size diameter of 12 to 14 cm (H₁) ranging from 1.55 to 5.11% throughout the storage study.
       
Interaction effect of date of sowing, variety and head diameter indicated significant variation in physiological loss in weight of broccoli during storage period. Lowest loss in weight (0.535 days after storage) was observed in Sadhana sown at 15^th September with 12 to 14 cm head (D₁V₂H₁). Weight losses were between 0.6 and 1.6% of original fresh weight supported by the findings of Jacobsson et al., (2004). Early shown crops had better PLW which may be attributed to the firm texture and good shape favoured by the good weather for growing while high temperature in the late sown crops leads to bit loose heads. Nath et al., (2011) showed results on PLW of broccoli florets indicated that weight loss was gradually increased. The maximum shelf life (19.67 days) of broccoli was recorded at 4°C (Roni et al., 2014) while our current research was emphasized for extension of shelf life through protective covering for 15 days at 5°C.
 
Marketability (%)
 
Marketability (%) was high in mid sown broccoli at 30th September compared to other date of sowing as shown in Table 1. Sadhana showed higher marketability than Aishwarya though both have fair marketability %. Small head diameter also gave higher marketability compared to other larger head diameter. Interaction effect of date of sowing, variety and head diameter gave highest marketability in Sadhana sown at 15th September and harvested at small head diameter of 12 to 14 cm. Weight loss in crop lead not only to physical weight loss but also leads to change in appearance, color, texture of produce whch ultimately decreases the market value as well as consumer preference (Pragya et al., 2020).
 
TSS (°B)
 
It was observed in Table 2 that TSS was maximum and constant (7.77°B in 5, 10 and 15 days after storage respectively) in early sown crop at 15^th September (D₁). Among the varieties considered, Aishwarya (V₁) exhibited higher TSS (7.82. 7.36 and 7.07°B on 5, 10 and 15 days after sowing respectively) compared to Sadhana (V₂). From Table 2, it was shown that among the various head diameters, medium size broccoli with 14 to 16cm diameter resulted higher TSS with 7.57, 7.38 and 7.24°B on 5,10 and 15 days after storage respectively.


       
Maximum TSS during storage was observed in Aishwarya sown early at 15^th September with medium head diameter of 12 to 14 cm (D₁V₁H₂). Loss in soluble solids during storage may be correlated with the finding of Ihl et al., (2001) where the soluble solid content decreased when sugar snap peas were stored at 5°C in sealed packages. Increasing trend in TSS in early sown crops may be supported by the findings of Mahfuzah et al., (2013) in packed strawberry while Galvao et al. (2008) reported that up to the first week of storage, marked reduction in soluble starch contents was observed in packed broccoli.
 
Ascorbic acid (mg/g)
 
Table 3 showed the maximum content in late sown crop at 15^th October (D₃) with 124.56, 109.86 and 96.75 mg/100 g during  storage period.


       
There was significant effect of variety on ascorbic acid content during the storage. Aishwarya (V₁) exhibited higher values (140.52, 128.71, 110.49 and 93.53 mg/100) from harvest to 15 days after storage respectively.
       
Head diameter showed significant effect on ascorbic acid during the storage study. Maximum ascorbic acid contents vary from 136.06 to 98.28 mg/100 throughout the storage period in early sown crops at 15^th September (H₁). Steady decrease in amount of ascorbic acid with storage period was evident in mushroom packed with modified atmosphere packaging unit after blanching followed by treatment with 2.5% calcium chloride, 3% citric acid and 0.1% sorbitol (Pallavi et al., 2020).
       
Considering the interaction effect in Table 3, the maximum values were recorded in Aishwarya sown at 15th September with 12 to 14 cm head (D₁V₁H₁). Broccoli sown at 15^th September (D₁) had the overall high amount of ascorbic acid during the period of study. Present study revealed that drastic change in ascorbic acid content has been reduced giving appreciable amount of ascorbic acid at the end of storage in refrigerated condition and according to studies conducted on different cultivars with distinct conditions, MAP was significantly effective to prevent drastic ascorbic acid loss in broccoli (Serrano et al., 2006, Carvalho and Clemente, 2004).
 
Chlorophyll (µg/g)
 
From the data analysed in Table 4, it was clear that date of sowing gave significant effect on chlorophyll content of broccoli during the storage period. Maximum chlorophyll content was observed in mid sown crop at 30th September (D₂) with 312.69, 305.53 and 298.52 µg/g on 5, 10 and 15days after storage while minimum chlorophyll contents of 275.33 to 242.22 µg/g during the storage period were noted in early sown crop at 15^th September (D₁).


       
Variety gave significant effect on chlorophyll content of broccoli during storage. Aishwarya (V₁) showed maximum values from 298.77 to 276.84 µg/g during the storage period while Sadhana (V₂) showed lower values from 289.48 to 258.41 µg/g during the period of the storage study.
       
It is revealed from Table 10 head diameter gave significant variation in chlorophyll content during the storage study. Large size broccoli gave higher chlorophyll contents (298.77, 281.16 and 276.84 µg/g on 5, 10 and 15 days after storage respectively) while small size broccoli (H₁) gave minimum chlorophyll contents (287.73, 265.87 and 251.05 µg/g on 5, 10 and 15 days after storage respectively).
       
Interaction effect of date of sowing, variety and head diameter gave significant effect on the chlorophyll contents of broccoli during the storage period resulting in maximum chlorophyll content (323.66 µg/g) during the storage period in Aishwarya sown at 30th September with head diameter 14 to 16 cm (D₂V₁H₂) while minimum chlorophyll contents (173.3 µg/g) were recorded in Aishwarya sown at 15th October with head diameter 12 to 14 cm (D₃V₁H₁). 
       
Maximum chlorophyll content was found in broccoli sown at 30th September, D₂ for the period of storage study while variety Aishwarya showed higher chlorophyll content than Sadhana. Since freshly harvested broccoli is composed by immature tissues, the inflorescence head shows rapid senescence and chlorophyll degradation (Clarke et al., 1994; Corcuff et al.1996). Decreasing trend of chlorophyll was supported by Nath et al., (2011) in broccoli florets which underwent chlorophyll degradation and a lower temperature resulted in less deterioration during post-harvest storage. The decrease in chlorophyll was supported by Rai et al., (2008) while Starzynska et al. (2003) reported that chlorophyll was degraded at a slower rate in the broccoli stored at 0°C.  
 
Yellowing percentage
 
Data presented in Table 5 indicated increasing yellowing % with the progress in storage period. Maximum yellowing of 14% was recorded in late sown broccoli at 15^th October (D³) while minimum yellowing in early sown crop 30^th September (D₁) ranging from 0.83 to 1.00% from day 5 to 15 days after storage.


       
It was clear from Table 5 that among the two varieties, Aishwarya (V₁) had higher amount of yellowing (0.55 to 8.04% throughout the storage period) during the storage period while larger broccoli head gave highest amount on yellowing on day 15 (16.89%) throughout the storage period.
       
Interaction among date of sowing and head diameter gave significant effect on yellowing % of broccoli during the storage period with minimum was observed in Aishwarya sown at 15^th October with 12 to 14 cm head, (D₃V₁H₁) which developed 1.33% yellowing at the end of storage period.
       
Broccoli sown at 15^th September D₁ had the maximum value of yellowing on the last day of storage and variety Aishwarya had more yellowing percentage than Sadhana. Small diameter broccoli had the least yellowing percentage at the end of storage while the best interaction effect was seen in Aishwarya sown at 30th September with 14 to 16 cm head D₂V₁H₂, Sadhana sown at 30th September with 12 to 14 cm (D₂V₂H₁). The decrease in chlorophyll due to loss of chlorophyll by retarding chlorophyllase activity was supported with the finding of Yan and Liu (2012). Schoutena et al., (2009) evaluated that for a number of broccoli heads, colour synthesis was larger than the colour decay during the storage period especially at 5°C in modified atmosphere which explained green colour is some treatments. Increase in yellowing colour score in packed broccoli during storage was supported by Beer and Crouch (2013).
 

Studying the various interaction effects of date of planting, variety and head diameter for harvest, it was shown that broccoli sown early i.e. 15th September gave quality in variety Sadhana with the smallest head diameter i.e., 12 to 14 cm since it possesses the most desirable criteria for marketability. The most common problem in post harvest management of broccoli was yellowing and it was shown clearly that yellowed broccoli still has appreciable amount of ascorbic and TSS content so it can be recommended for consumption even though there is less acceptance in market due to unawareness about the nutrient content.