PhD

Avocado is a subtropical fruit crop, belonging to the family Lauraceae, and is
rich in proteins, vitamins, minerals and monounsaturated fatty acids such as oleic acid,
contributing to its high nutritive and therapeutic value. Even though there are a large
number of genotypes with widely varying characteristics, inadequate characterisation
and identification result in the lack of awareness, improper utilisation and insufficient
post harvest management of avocado. Hence, the present study titled, „Post harvest
characterisation and management of avocado (Persea americana Mill.)‟ was carried
out in the Department of Post Harvest Technology, College of Agriculture,
Vellanikkara during 2018-2021. The main objectives of the study were to characterise
avocado accessions collected from different parts of Kerala and to evaluate the effect
of post harvest management practices to extend the shelf life of avocado fruits and to
study the effect of food additives on the quality of frozen slices, fruit pulp, freeze dried
fruit powder and subsequently to standardise an instant avocado fruit shake.
For the characterisation of avocado genotypes, 27 accessions were collected,
among which 14 accessions were from RARS, Ambalavayal in Wayanad and 12 from
Kanthaloor in Idukki and one accession was collected from Thanniyam in Thrissur.
Characterisation of avocado genotypes based on the horticultural and biochemical
traits, accession 25 from Idukki had comparatively higher TSS, vitamin C, total
carbohydrates, total flavonoids, oleic acid, calcium, potassium, iron, total ash and crude
fibre content. Hence, accession 25 was selected for subsequent post harvest
management studies. Antioxidant activity of the methanolic extract of fresh fruit of
accession 25 was evaluated by DPPH, FRAP and ABTS assays. Greatest free radical
scavenging activity was observed in ABTS assay with lowest IC50 value of 0.10 μg/mL.
Fresh and mature avocado fruits, surface sanitised with 2 ppm ozone and pretreated with 2 % calcium chloride, followed by shrink packaging with 25 μ polyolefin
film and subsequently stored in refrigeration (T8) as well as cool chamber (T9) were
found to be the ideal storage conditions with longest shelf life of 27 days. Calcium
chloride pre-treated fruits with shrink packaging, stored under refrigeration had lowest
physiological lossin weight, respiration rate, ethylene evolution rate and decay per cent,
with better retention of firmness. Fruits of this treatment retained significantly higher
total carbohydrates, total protein and total phenols during storage.
Avocado slices pre-treated with 40 % sucrose, ascorbic acid (0.5 %) and
potassium metabisulphite (0.1 %), quick frozen to -20 ºCin 30 minutes followed by
packing in 200 gauge LDPE pouches and held under frozen temperature (-18 0C) was
the most ideal pre-treatment for storage. This treatment recorded significantly higher
TSS, vitamin C, total carbohydrates, total protein and organoleptic acceptability
throughout storage and lowest water activity, peroxide value and microbial population.
For preparation and storage of avocado pulp, pre-treatments with ascorbic acid
(0.5%) and KMS (0.1%) followed by vacuum packaging LDPE bags (T10) as well as in
glass jars (T12), stored under refrigeration resulted in longest shelf life and better
quality. Total protein, total phenols, total carbohydrate, total fat, viscosity and
organoleptic scores were highest in these treatments with lowest water activity,
polyphenol oxidase activity and microbial population during storage.
For preparation of avocado fruit powder, addition of 5% maltodextrin, ascorbic
acid (1%), tricalcium phosphate (0.15%), EDTA (0.05%) and potassium sorbate
(0.05%) followed by freeze drying at -70 ºCand 100 mtorr vacuum for 36 hours
followed by packing in LDPE laminated aluminium pouches (T14) and glass jars (T16)
stored under refrigeration were the ideal methods with longest shelf life and quality.
Significantly higher bulk density, solubility, colour value L*, TSS, vitamin C, total
carbohydrates, total fat and organoleptic scores were recorded in these treatments
during storage along with lowest hygroscopicity, colour value a* and b*, peroxide
value, water activity and microbial population.
An instant avocado shake was standardised by combining avocado fruit powder
with skimmed milk powder, sucrose and water in the proportion of 1:2:1:2 with
appealing appearance, light yellowish colour, unique blend of taste and flavour of
avocado fruit and skimmed milk powder.