Browsing by Author "Gunawardhane, L.K.A."

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    Development of Avocado (Persea americana) Incorporated Set Yoghurt
    (Uva Wellassa University of Sri Lanka, 2015) Kulasinghe, W.M.A.A.; Abesinghe, A.M.N.L.; Gunawardhane, L.K.A.
    Yoghurt is one of the best known of all cultured-milk products in the world. According to SLS standards (1989) Streptococcus thermophillus and Lactobacillus bulgaricus are used to convert lactose in milk in to lactic acid during yoghurt production. Fruit yoghurt is produce by adding fruits and their nectars, jams, marmalade, fruit jellies, fruit drinks, fruit syrups and concentrated fruit drinks to yoghurt or cultured pasteurized milk and fruit yoghurts enhances versatility of taste, color and texture for the consumer (Chandan and Shahani, 1993). Avocado (Persea americana) is a fruit which is having a very good nutrient profile and thus incorporation endorses the healthy image of yoghurts. However, incorporation of avocado in to set yoghurt is limited by enzymatic browning or formation of brown color melaniodins from polyphenol oxidase enzyme in avocado (Bindesh, 2010). Pauker et al. (1992) have found incorporation of avocado in to yogurt in the form of fresh avocado pulp is impossible due to enzymatic browning. Therefore, control of enzymatic browning is essential in producing avocado incorporated set yoghurt. Current study was carried out to develop avocado incorporated set yoghurt that is having an adjusted solid content based on sensory properties and controlling enzymatic browning of avocado pulp. Methodology Market available fresh ripened avocados (Fuerte variety) were manually peeled and crushed in to a smooth pulp. It was divided in to seven samples with same weight and preserved using several preserving and enzymatic browning control methods such as 1% citric acid, 1% (w/w) ascorbic acid (Patricia et al., 1993), 1% (w/w) citric acid and 1% (w/w) ascorbic acid together (Lopez, 2001), 0.1% (w/w) sodium benzoate (Patricia et al., 1993), 0.1% (w/w) potassium sorbate (Singha, 2011), heat treatment at 40 ºC temperature for 30 minutes (Cantwell, 1992) and preparation of avocado pulp as a jam (Connelly, 2013). The best avocado pulp preserving method (least color changing treatment) was selected by conducting a sensory evaluation using 30 untrained panelists. The selected method of preserving avocado pulp (avocado jam) was used in preparation of avocado incorporated set yoghurt. Yoghurt mix preparation was done according to Pande (2010). Preliminary trials were used to select the appropriate level of ingredients (avocado jam, sugar and gelatin). Sugar and gelatin levels were finalized after having several sensory trials using 30 untrained panelists. Potassium sorbate 0.03% (w/w) was added to the final mixture as preservative (SLS Standards, 1989) and homogenized using a beater (National™, MK-H100N). Inoculation of lactic acid bacteria culture of YC 350 freeze dried (DVS) was done at 45 °C temperature. Then mixture was poured in to 80 mL plastic yoghurt cups and incubated at 42 ±2 ˚C for 4 hours. Each treatment consisted with three replicates. Total plate count, coliform bacteria count, yeast and mold count, pH, titratable acidity and peroxide value of selected avocado incorporated set yoghurt and avocado jam was tested at day under refrigerated storage. A proximate analysis was done to determine the composition of the avocado incorporated set yoghurt. Results and Discussion Addition of 50% (w/w) sugar in to avocado pulp showed lowest brown color development (P<0.05). Added sugar may have reduced the water activity of the avocado pulp. Enzymes require certain level of water in their structures to maintain their natural conformation, allowing them to deliver their full functionality. Therefore, presence of 50% sugar inhibits the activity of polyphenol oxidase enzyme. Adding more than 50% of sugar, crystalize sugar in the avocado pulp which gives undesirable consistency. Twenty percent of avocado jam incorporation level shows the best results according to the sensory evaluation (P<0.05). Total plate count, yeast and mold and coliform counts of the avocado incorporated set yoghurt were not exceeding SLS standards for set yoghurt during 11 days of refrigerated storage. Titratable acid percentage of avocado jam has increased from 1.22±0.07 to 1.4±0.07 during day 1 to day 11 (P<0.05). It may be due to conversion of fermentable sugars in to acids by microorganisms available in avocado jam. Further, titratable acid percentage of avocado incorporated set yoghurt increased from 0.86±0.03 to 0.94±0.03 during 11 days storage period (P<0.05). This is due to the presence of live lactic acid bacteria in culture which ferment lactose in milk to lactic acid with the time (Chandan and Kilara, 2013). pH of avocado jam and pH of avocado incorporated set yoghurt was reduced from 3.52±0.06 to 3.35±0.06 and from 4±0.03 to 3.91±0.03, respectively during day 1 to day11. Increasing acidity results in decreasing pH level in the product. No fatty acid oxidation was detected in the avocado jam during storage period of 11 days. Avocado incorporated set yoghurt started free radicle formation and rancidity development day of storage onwards. Moreover, it shows increasing browning effect. Since, avocado is a fruit with high fat and it contains considerable level of fatty acids, there is a potential to observe oxidation in this product. Statistical analysis showed that enzymatic browning has an influence on the increment of changing rapidity of titratable acidity, pH and peroxide value. Further, it showed fatty acid oxidation and pH are not related. In the view of avocado incorporated set yoghurt and avocado jam, avocado jam is having very low water activity due to saturated sugar solution. Avocado incorporated set yoghurt is having an environment with increasing acidity and decreasing pH with lactic acid fermentation. Water activity of avocado incorporated set yoghurt also very high compared to avocado jam. These factors may have influenced on the observed color change in avocado incorporated set yoghurt. Proximate analysis of avocado incorporated set yoghurt showed that there is a significant difference with plain yoghurt (P<0.05). Fat (3.6±0.42%), fiber (0.3±0.21%), ash (0.9±0.14%), protein (3.5±0.07%) and total solids (16.10±1.31%) in avocado incorporated set yoghurt is comparatively higher than available fat (3.0±0.42%), fiber (00±0.21%), ash (0.7±0.14%), protein (3.4±0.07%) and solids (14.24±1.31%) in plain yoghurt. Conclusion Avocado incorporated set yoghurt is more nutritious compared to set yoghurt as it has included with more protein, minerals and fiber. There is a relationship between enzymatic browning and fatty acid oxidation. Further studies are required to identify how enzymatic browning and fatty acid oxidation relates with each other and to extend the shelf life of avocado incorporated set yoghurt.
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    Development of drinking yoghurt by incorporating corn (Zea mays) milk and corn seeds
    (Uva Wellassa University of Sri Lanka, 2015) Mendis, R.I.W.; Abesinghe, A.M.N.L.; Samaraweera, A.M.; Gunawardhane, L.K.A.
    Cereal grains are considered as important sources of dietary proteins, carbohydrates, vitamins, minerals and fiber for people all over the world (Chavan and Kadam, 1989). Corn (Zea mays) is locally grown cereal that can be purchased at low price from several areas in Sri Lanka. Corn milk is considered as a new innovation, especially in making yoghurt based products. Vegetable based corn milk yoghurt is an alternative to substitute the cow milk based yoghurt. Drinking yogurt is the fastest growing food and beverage category in worldwide (Yasni and Maulidya, 2013). However, still value added drinking yoghurts are rare in Sri Lankan market. Adding cereal grains is a perfect way to upgrade a drink to a nutritious breakfast. Therefore, this study was conducted to develop yoghurt by incorporating corn (Zea mays) milk and corn seed to cow milk. Methodology The study was carried out at Lucky Lanka Milk Processing Com. Ltd (LLMP), Matara and Uva Wellassa University. Six experimental trials with different treatments were conducted. In trial I, mature fresh corn seeds, mature boiled corn seeds and germinated corn seeds were separately used to extract corn milk and the best extract of corn milk was evaluated by sensory properties (odor, taste, color and mouth feel) using untrained panelist. In trial II the most compatible sugar (8%, 9% and 10% w/v) and gelatin (0%, 0.2% and 0.4% w/v) levels for different corn milk percentages (5%, 10%, 15% and 20% w/v) were identified. After selection of appropriate combinations of sugar and gelatin levels, trial III was done to select the best corn milk incorporation level by narrow downing the corn milk percentages (6%, 8%, 10%, 12% and 14%). Preserved in sugar syrup and boiled corn seeds were crushed into two sizes (> 3.15 mm and 2 mm –3. 15 mm) to prepare different types of corn seeds. Trial IV was carried out to select best corn seeds particles on the textural basis and trial V was done to assess the consumer acceptability for the presence of corn seeds in the corn milk incorporated drinking yoghurt. Finally three treatments (trial VI) were prepared and evaluated on sensory, chemical and microbiological properties. The sensory evaluation was done using 35 untrained panelists. In chemical analysis, proximate analysis (moisture content, crude fat, total solid, crude protein, ash and crude fiber content) was conducted. pH value and titratable acidity were evaluated and microbiological analysis was done for Yeast and Moulds, and Escherichia coli for three weeks in one day interval. The sensory data were analyzed using Friedman nonparametric test. Complete Randomized Design was conducted and data obtained from chemical and microbiological tests were analyzed by Analysis of Variance using the General Linear Model procedure of SAS. Significant means of treatments were separated using the Least Significant Difference test (P< 0.05). Result and Discussion In trial I, boiled corn seeds (mature) based method was selected to extract corn milk. Other two methods were rejected due to the unpleasant odour and taste which may be due to the activation of various food enzymes and breaking down the higher molecular components to simple molecules during germination. Eight per cent sugar (w/v) for 5% corn milk (w/v) and 10% sugar (w/v) for other 10%, 15% and 20% corn milk (w/v) incorporation levels were selected due to desirable sweetness. The gelatin level (w/v) was selected as 0% due to the presence of appropriate drinking yoghurt properties including texture, mouth feel, appearance and viscosity. The whey separation has been prevented by stabilizing effect of corn starch in corn milk. In sensory evaluation, 8% corn milk incorporation level was significantly highly preferred by panelist with respect to mouth feel, taste and overall acceptability (P<0.05). However, there is no significant difference in color and aroma of the three treatments (P>0.05) (Figure 01). Addition of corn milk had no influence to change colour and aroma of the product. Overall acceptabilty 6 4 2 0 Aroma 7% corn milk incorporation level 8% corn milk incorporation level Taste Mouth feel 9% corn milk incorporation level Figure 01. Web diagram for level of corn milk incorporation in sensory evaluation In trial IV, sugar syrup based method was rejected due to hardness of the seeds and crushed boiled corn seeds were selected. Further, the sensory results revealed that the preference (taste, aroma, mouth feel, color and overall acceptability) for corn seeds >3.15 mm or 2 mm to 3.15 mm particles incorporated drinking yoghurt is less whereas preference for corn milk incorporated drinking yoghurt without corn seeds was high. The observed difference is due to the disturbance for the drinkable property of product by presence of corn seed particles. The composition of the selected corn milk incorporated drinking yogurt is given in Table 01. There was a significant difference between treatments for change in pH with the storage period (P<0.05). pH values of the T8 (with preservative) and control were not changed dramatically. Control of pH by potassium sorbate could be due to inhibition of the activity of starter culture by inhibiting various enzymes in microbial cell (Rajapaksha et al., 2013). There was a significant difference between treatments with respect to acidity (P<0.05) and titratable acidity increased significantly with storage period and in treatments without preservatives. According to Rajapaksha et al. (2013), titratable acidity of yogurts increased over the time and acidity of yoghurt without potassium sorbate increases drastically than other treatments reflecting the inhibitory activity of potassium sorbate on post fermentation. Table 01. Composition of select corn milk incorporated drinking yoghurt Raw material Percentage Quantity (g) Milk 79.54% 867.03 Dairy cream 1.03% 11.33 SMP 1.42% 15.49 Corn milk 8.00% 87.20 Sugar 10.00% 109.00 Total 100.00% 1090.00 There were no contaminations with Coliform and Escherichia coli and thus safe for human consumption. There were no yeast colonies in T8 and control sample. At day 11, yeast colonies were exceed the SLS standards of <1000 only in T7 (without preservative). Proximate analysis revealed all the physiochemical characteristics of corn incorporated drinking yogurt (protein, fat, ash, fiber and total solid), except moisture significantly higher compared to plain drinking yoghurt (P<0.05). Usually drinking yoghurt does not contain fiber. However, due to addition of corn, milk fiber was increased up to 0.5%. Conclusion Eight per cent corn milk incorporation level with selected sugar (10%) and gelatin (0%) level has best consumer preference with respect to the taste, mouth feel and overall acceptability (P<0.05). Moreover, drinking yoghurt without corn seed particles is preferred by the panelists. Shelf life of product without potassium sorbate is around 11 days at 4 ºC with respect to microbiological analysis and physiochemical analysis.