Exercise

Practical 4 - Estimation of moisture content

Aim: To determine the moisture content in fresh and processed products

Theory: Estimation of moisture in fresh and processed fruit and vegetable products is important for evaluating their nutritive composition as well as to optimize method for their processing like drying, preparation of different products viz jams, preserve, candies etc. Moisture is determined by drying the weighed sample to a constant weight in hot air oven and measuring the loss in weight to express the moisture content in per cent. This method is used for estimation of moisture in all food products which do not decompose at 100ºC. Moisture content of some commodities (Table 4.1) is as under:

Table 4.1: Moisture content of some fruits, vegetables and food products.

Commodity/ products

Moisture (%)

Apple

85-90

Avocado

65

Berries

81-90

Citrus fruit

86-89

Guava

81

Lima beans ( Green

67

Melons

92-94

Olives

72-75

Raw nuts

3-5

Radish

93

Sweet potato

69

Honey

20

Grape juice

70-85

Lime juice

89-90.3

Lemon Juice

81.1-92.4

Fruit juices and nectars

85-93

Fruit Jellies, jams, Marmalade and preserve

30-35

Syrups

20-40








































Apparatus/equipments/ machinery required
  • Hot air Oven
  • Weighing balance
  • Moisture dishes/Petri plate
  • Desiccators
Procedure for determination: Moisture content may be determined by
  1. Drying in an oven
  2. By distillation with an immiscible solvent
  3. Chemical and physical methods
Procedure:
  • Dry flat bottom metallic dish or Petri plate at 100oC for 1 hr, cover the dish, cool and weigh. (w0)
    • Spread 10-20g sample (or 1.5g for dried products) uniformly on to the Petri dish and weigh (w1).
    • Remove the cover and dry in hot air oven at atmospheric pressure. Maintain temperature at 70oC for fruits and their products or 1000C in case of vegetables and their products.
    • Dry till constant weight is achieved. 16-18hrs are sufficient for most of the commodities
    • After drying replace lid, cool in desiccators and reweigh (dish containing dried sample).
  • Ensure that the constant weight is achieved.
  • Calculate moisture content as under:
W2 – W0
Moisture, % = -------------------× 100
W1 – W0

Total solids (%) = 100 – Moisture (%)


Observations

Sample No.

Weight of sample taken

Weight of sample + weight of moisture/petri dish

Weight of dried sample + weight of moisture/petri dish

Loss in Weight

1





2





3





Mean






Calculation
(Wt of fresh sample+ moisture dish) – (Wt of dried sample+ moisture dish)
Moisture (%) = ----------------------------------------------------------------------------------- x 100
Weight of sample

Total solids (%) = 100 – Moisture %
Last modified: Wednesday, 7 March 2012, 8:54 AM