Table 1 Maturity indices of selected fruits and vegetables and their methods to determine (Prasad et al. 2018)

Non-Destructive

Fruits/Vegetables

Methods

    Calendar date

All fruits

    Size and Shape

All fruit, beans, carrot, cucumber, cheery asparagus, and cauliflower

Vernier Calliper

    Colour

All fruits, tomato, muskmelon, apple, pears, mango, papaya and watermelon

Munsell Colour chart, Colourimetry

    Specific Gravity

Cherries, Mango

Displacement Method (Archimedes principle)

    Optical Properties

Apple, Tomato

NMR, NIR, Raman Spectroscopy, UV–VIS Spectroscopy and Thermal Imaging

    Surface Morphology

Grape (cuticle formation), banana, and litchi

Magnetic Resonance Imaging (MRI) and Surface Electron Microscope (SEM)

Destructive Method

    TSS

All fruits, tomatoes, and melons

Hand held Refractometer, Abbey’s Refractometer

    Firmness/Texture

Pome and stone fruits, beans, lettuce, and muskmelon

Penetrometer, Universal Texture Analyzer, Pressure Gauge

    Juice Content

Citrus fruits

Volume

    Titrable Acidity

Pomegranate, citrus fruits, papaya, and kiwifruit

Analytical Chemistry

    Oil Content

Avocado

Soxhlet Apparatus

    Moisture content

All fruits

Karl fischer method and Conventional Hot Air Oven

    Volatile compounds Naringin, Limonene (Bitterness)  Tannin (Astringency)

Citrus fruits Persimmon and dates

GCMS, LCMS, HPLC, Spectrophotometer

    Sugar

Pome, stone fruits, and grape

Alcohol Test, Phenol -sulphuric acid for reducing sugar

    Respiration Rate (Ethylene Content

Apple and pears

Biosenser connected tom respirator chamber