Fruit Flavored Yoghurt: Chemical, Functional and Rheological Properties

Yoghurt is a coagulated milk product that results from the fermentation of lactose in milk by lactobacillus bulgaricus and streptococcusthermphillus (Bourlioux and Pochart, 1988). Other lactic acid bacteria (LAB) are also frequently used to produce yoghurt with unique characteristics (Adolfsson et al., 2004) 

Yogurt consumption has increased around the world because of its nutritional value, therapeutic effects, and functional properties (McKinley, 2005). The use of different fruits and additives in fruit yogurt production has improved its nutritional and sensory properties (Cakmakcı et al., 2012). 

Peaches, cherries, apricots, papaya, cactus pear and blueberries are frequently used in yogurt production (Arslan and Ozel, 2012). Yoghurt is an increasingly popular cultured dairy product in most countries. This is partly because of an increased awareness of the consumers regarding possible health benefits of yoghurt. Yoghurt is easily digested, has high nutritional value, and is a rich source of carbohydrates, protein, fat, vitamins, calcium, and phosphorus. Because milk protein, fat, and lactose components undergo partial hydrolysis during fermentation, yoghurt is an easily digested product of milk (Sanchez et al., 2000). 

The flavors are key factors for food stuff acceptability by consumers. Organoleptic evaluations have shown a marked preference for the fruity yoghurt (Barnes et al., 1991). Addition of different fruit in yogurt manufacture has been attempted increasingly. Use of fruit in yogurt makes its more delicious. This product contains both the refreshing flavor of fruit and beneficial effect of yogurt. Fruit yogurt has more taste and pleasing flavor (Mahmood et al., 2008)

 The pectin and sugars from the fruit are mixed with the yoghurt, causing an increase in its consistency and viscosity and therefore mouth fell is improved (Nongonierma et al., 2007). 

Pectins are added to acidified dairy products to avoid syneresis (Tromp et al., 2004)They adsorb on casein reversibly, inducing an increase in the steric repulsion and thus decreased their aggregation (Nongonierma et al., 2007). 

Introduction of various fruit-flavoured yoghurts has significantly contributed to the consumption of yoghurt from all ages. Fruits may be added to yoghurt formulae as single or blends in the form of refrigerated, frozen, canned fruit, juice or syrup. Most common fruits used in yoghurt formulae are peach, cherry, orange, lemons, purple plum, boysen berry, spiced apple, apricot, pineapple, strawberry, raspberry and blueberry (Chandan et al., 1993). Incorporation of fruits endorses the healthy image of yoghurts. In contrast to the study dealing with the health influences of the addition of fruit, there is a very limited research about the technological, physicochemical, organoleptic, and microbiological properties of fruit-added yoghurts (Bardale et al., 1986). 

Carica papaya belongs to the small family Caricaceae and is one of the non-seasonal and evergreen fruits in Malaysia. There is always a soft main trunk and tufted leaves at the top. Papaya varies in sizes, shape, color and taste. In Malaysia, the preference is for the red-fleshed varieties namely Eksotika. The skin color of papaya is usual green when immature, changing to fully reddish-orange when fully ripened. The changed in outer color of the skin of fruit is an indicator of ripeness, and this change is considered mainly due to an increase in the carotene content and a decrease in chlorophyll. The color of papaya fruit flesh is determined largely by the presence of carotenoid pigments. Red-fleshed papaya fruit contain lycopene, whilst this pigment is absent from yellow-fleshed fruit ( Devitt et al., 2010) . The red-fleshed papaya has 63.5% of total carotenoids as lycopene which is absent in yellow-fleshed fruit 

 (Yamamotohy, 1964). Papaya contains a broad spectrum of phytochemicals including enzymes (in the latex), carotenoids (in fruits and seeds), alkaloids (in leaves), phenolics (in fruits, leaves, and shoots), and glucosinolates (in seeds and fruits).

 Cactus pear (Opuntia spp.) is a tropical fruit tree, native to America, which grows in arid and semiaridregions (PimientaBarrios & del Castillo, 2002). There are green fruits and also coloured fruits (red, yellow or purple) due to the presence of various pigments such as betalains and carotenes (Tesoriere et al., 2005). This fruit is abundantly found in Mexico and United States, but also grown in North Africa, Madagascar, Australia, Srilanka and India (Piga, 2004). Prickly pear fruit (PPF) can be considered a food of nutraceutical and functional importance due to its high content of chemical constituents characterized bynutritional and health improving properties. 

Generally, Prickly pear fruit (PPF) is rich in pectin, mucilage and minerals, whereas the fruits are good sources of vitamins, and amino acids. The pulp of prickly pear could be processed into many different products such as marmalades, jellies, natural sweeteners, wines and other alcoholic beverages, candies, canned, frozen fruit, etc. (Sawaya et al., 1983; Ewaidah and Hassan, 1992; Barbera, 1995; Saenz Hernandez, 1995; Gurrieri et al., 2000; Saenz, 2000; Sepulveda et al., 2000; AbdelNabey, 2001; Moßhammer et al., 2006).