Processing of Horticultural Crops (1+2)

Exercise

Practical 3 - Determination of total Soluble Solids

Aim: To determine the total soluble solids in fresh and processed fruit and vegetable products.

Theory and Principle: Total soluble solids (TSS) are determined by means of brix hydrometers which measures the specific gravity or by using hand refractometer which measures refractive index. Brix is a measure of soluble solids only in case of pure sucrose solutions. Generally, the fruit juices contain more sugar than any other soluble constituent and hence, brix provides a useful guide of soluble solids or sugar contents. Brix hydrometer is used to determine the percentage of brix in syrup while Abbe refractometer gives refractive index as well as degree brix. The Refractive index of the test solution is measured at 20°C using a refractometer and the soluble solid content is determined by the use of tables correlating refractive index with soluble solids. Generally, hand refractometer is used for determining TSS in food samples in fruit processing units. TSS of different products varies as under:

Fruit products	TSS(oB)
Most fruit juices	10-15
Perlette grape juice	11-18
Lime juice	6-14
Lemon Juice	5-9
Sauces	Not less than15
Ketchup	Not less than25
Squashes	Not less than 40
Jam	Not less than 68
Jelly and Marmalade	Not less than 65
Syrups/Sharbats	Not less than 65
Preserve and Candies	Not less than 68

Apparatus/machinery/equipments required:

• Hand refractometer
• Abbe-refractometer
• Distilled water

Procedure for estimation

1. Calibrate the refractometer with a drop of distilled water, adjust the scale to 0 %
2. Wipe the prism with a cotton swab.
3. i) Cut a piece of fruit and squeeze a drop of juice on the prism of the refractometer.

ii) Place a drop of juice/squash/syrup on the prism.

iii) Place small quantity of jam/jelly in muslin cloth and squeeze and place on the prism.

4. Read the value directly through eye piece of refractometer towards the light at room temperature.
5. Correct the readings to standard temperature of 20°C if readings are made at temperature other than 20^oC (Table 3.1)

Table 3.1: Temperature correction for the standard model of sugar refractometer calibrated at 20^oC

Temperature 0C	Scale reading for soluble solids contents, %
	5	10	15	20	25	30	40	50	60	70
	Corrections to be subtracted
15	0.29	0.31	0.33	0.34	0.34	0.35	0.37	0.38	0.39	0.40
16	0.24	0.25	0.26	0.27	0.28	0.28	0.30	0.30	0.31	0.32
17	0.18	0.19	0.20	0.21	0.21	0.21	0.22	0.23	0.23	0.24
18	0.13	0.13	0.14	0.14	0.14	0.15	0.15	0.15	0.16	0.16
19	0.06	0.06	0.07	0.07	0.07	0.07	0.08	0.08	0.08	0.08
	Corrections to be added
21	0.07	0.07	0.07	0.07	0.08	0.08	0.08	0.08	0.08	0.08
22	0.13	0.14	0.14	0.15	0.15	0.15	0.15	0.16	0.16	0.16
23	0.20	0.21	0.22	0.22	0.23	0.23	0.23	0.24	0.24	0.24
24	0.27	0.28	0.29	0.30	0.30	0.31	0.31	0.31	0.32	0.32
25	0.35	0.36	0.37	0.38	0.38	0.39	0.40	0.40	0.40	0.40

Inference: Most fresh fruits generally contain TSS between 10-18^oB except limes and lemons which may contain less TSS. Squashes have TSS more than 40^oB while Jams contain TSS above 68^oB. For determining TSS of dried products, the sample is diluted in known quantity of distilled water and observed reading is multiplied with the factor.