Module 4. Fruits and vegetables juice processing

Lesson 14

PROCESSING OF SELECTED FRUIT JUICES-I

14.1  Introduction

Fruit are one of the most popular natural food that is highly nutritious and enticing. People are now craving for fruit juices/beverages in ‘ready-to-drink’ form. The shelf life of fruit is limited; they tend to decay with progress of ripening. Concentration of fruit juice, freezing, individual quick freezing, osmotic dehydration, dehydration to obtain fruit powders are some to the methods being used to counteract the limited shelf life of fruit. The fruit as slices/chunks/candied or even as juice/pulps/concentrates are used in food industry viz. ice cream, fruit yoghurt, fruit cakes, fruit bread, etc.

14.1.1 Classification of fruit juices

Food Safety and Standards Act (FSSA) has laid down specifications for various types of fruit juice beverages including nectars (Figures 14.1 and 14.2).

Table 14.1 FSSA specifications for various types of fruit beverages.

No.

Name of the product

Fruit juice/puree in the final product (%), Min.

Total Soluble Solids %, Min.

Acidity expressed as citric acid, Max

1.

Squash

25

40

3.5

2.

Crush

25

55

3.5

3.

Fruit Syrup/Fruit Sherbats

25

65

3.5

4.

Cordial

25

30

3.5

 

Table 14.2 FSSA specifications for nectars.

Type of Nectars

TSS (%), Min.

 

Fruit Juice

Content (%), Min.

Acidity expressed as

Citric Acid (%), Max.

Orange Nectar

15

40

1.5

Grape Fruit Nectar

15

20

1.5

Pineapple Nectar

15

40

1.5

Mango Nectar

15

20

1.5

Guava Nectar

15

20

1.5

Peach Nectar

15

20

1.5

Pear Nectar

15

20

1.5

Apricot Nectar

15

20

1.5

Non-pulpy Black Currant Nectar

15

20

1.5

Other Fruit Nectars

15

20

1.5

Other Fruit Nectars of High Acidity/Pulpy / Strong flavour

15

20

1.5

Mixed Fruit Nectar

15

20

1.5

 

In this lesson we will be discussing Orange, Grapefruit, Lemon and lime juices.

14.2  Grapefruit – Botanical name -  Citrus paradise

Two main varieties include :

  1. White grapefruit – ‘Duncan’ and ‘Marsh’. The seedless Marsh is the most popular. The Duncan variety has best flavor.
  2. Pink or pigmented grapefruit – ‘Red blush’ and ‘Star Ruby’ – both contains red pigment lycopene.

14.3  Lemon – Botanical name – Citrus limon (L).

Two varieties are very popular viz., ‘Eureka’ lemon and ‘Lisbon’ lemon.

Mesero lemon of Italy is best processing lemon in the world.

14.4  Lime – Three types – small fruited one is Citrus aurantifolia, large-fruited one is Citrus latifolia and Sweet lime is Citrus limettoides.

Indian lime is sweeter than other limes and popular in India and Pakistan.

Lime is greener in color than lemons, both on the exterior and interior of the fruit.

14.5  Production of Citrus Juices

Fig. 14.1 Flow chart for preparation of Grapefruit juice

The lemon oil is more valuable than that of orange oil due to high aldehyde (2-4% aldehydes viz., citral – a mixture of neral and geranial) in lemon oil.

Grapefruit oil comprises of terpene thiols and nootkatone, which gives characteristic flavor and aroma to the oil.

FMC system uses Desludger to separate slurry into ‘oil-rich emulsion’, which removes ol from the fruit peel at the juice extractor.

The extent of heat treatment given to juices is important since it should deactivate the pectinase (pectin methyl esterase). Further heating should be avoided to prevent hydrolysis of pectin and sugar, which may result in cloud loss and gelation. If pectic enzyme is inactivated, it avoids separation of two layers viz., pulpy lower one and clear upper one in extracted juice.

14.5.1  Deaeration of juice

Single strength lemon juice even when stored under low temperature undergoes significant degradation, depending on the essential oil content. If oxygen is absorbed in juice during processing, it causes decay, ascorbic acid is oxidized. d-limonene is attacked with the formation of terebenthic taste.

14.5.2  Deoiling of juice

About 5-6% of juice is transformed to vapour at 50oC; there is 80% removal of essential oil plus removal of air. The non-terpenic aromatic fractions are condensed and reintroduced. The oily phase is separated by centrifugation or decantation.

14.6  Orange Juice

The scientific name of Sweet Orange is Citrus sinensis. Some varieties of Orange include Sathgudi, Mosambi, Malta; The exotic varieties being Jaffa, Hamlin, Pineapple, Valencia, etc.

14.6.1  BIS Standard: Orange juice shall be obtained by a mechanical process from the endocarp of ripe, sound mandarine or oranges or by reconstituting orange juice. The juice shall have characteristic bitter taste, clean aroma and flavour (free from fermented flavour). The additives permitted include peel oil, orange essence and flavour, sugar, invert sugar and/or liquid glucose. It should be free from preservatives.                                                                                                                

Table 14.3 BIS requirements for Orange juice

Particulars

Requirement

Brix of clear sample

Min. 10.0

Acidity

0.25 – 1.0% as anhydrous citric acid

Essential oil

Max. 0.3 ml (based on weight)

14.6.2  Bitterness in juice     

Limonin is the main bitter fraction of ‘Navel’ oranges. The non bitter monolactone of limonic acid gets rapidly converted to bitter tasting dilactone i.e. limonin at pH of about 3.0. Delayed bitterness is due to chemical change i.e. conversion of nonbitter precursor to bitter compounds by the process of extraction of the juice.

14.6.3  Other means to prevent bitterness of orange juice