Abstract:
Yoghurt and cheese are the common dairy products consumed in Nigeria, but they are highly susceptible to deterioration during storage. Natural preservatives are generally preferred to synthetic ones which are likely to be hazardous to human health. Literature is sparse on utilisation of African cardamom and turmeric in preservation of yoghurt and cheese. This study was designed to evaluate the potentials of African cardamom and turmeric in yoghurt and cheese preservation.
Milk was produced from soursop fruit using standard methods. Milk samples were collected from three-year old Sokoto Gudali (cow) and Red Sokoto (goat) at 7.00–8.00am daily and the samples were maintained at low temperature (-4oC) using ice-cubes. Yoghurts and cheese were produced from the milks using established procedures. Lactic Acid Bacteria (LAB) from soursop, cow and goat milk yoghurts and cheese were isolated, identified and characterised using 16S rDNA molecular procedure. The LAB isolates were used as single or multiple-strain starter culture in yoghurt production. Yoghurt and cheese samples were preserved by equal proportion mixtures of aqeous extract (10g of spices dissolved in 100ml distilled water and centrifuged) of Aframomum danielli and Curcuma longa at 1.0%, 1.5%, 2.0% and 2.5% concentrations, and control for 12 weeks at refrigeration temperature (4oC) and analysed biweekly for chemical (soluble solids, pH, total titratable acidity), proximate, mineral and microbiological (total plate and yeast counts) properties. Sensory attributes of the samples were determined using 9-point hedonic scale. Data were analysed using ANOVA at α0.05.
Five Lactobacillus spp were isolated and identified as Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus licheniformis, Bacillus subtilisand Lactobacillus rhamnosus. The mixture of Lactobacillus fermentum and Lactobacillus licheniformis produce best quality yoghurt in terms of chemical characteristics. The yoghurts contained protein (0.92-8.75%), fat (0.02-9.90%), ash (0.55-1.23%), moisture (73.43-91.87%) and carbohydrate contents (5.18-6.61%). Cheese had protein (13.04±0.02), fat (16.01±0.01), ash (1.60±0.02), moisture (55.81±0.04) and carbohydrate contents (13.54±0.02). Major mineral contents in yoghurt samples were calcium, magnesium, potassium, sodium, iron and zinc ranged from 40.07-640.75, 25.75-31.95, 869.50-2454.75, 60.00-85.00, 7.85-15.35 and 0.48-0.61 mg/100mL, respectively. Mineral contents in cheese were calcium, magnesium, potassium, sodium, iron and zinc ranged from 223.00±0.07, 37.00±0.01, 260.00±0.03, 17.00±0.00, 1.20±0.06 and 1.90±0.05 mg/100mL, respectively. Soluble solids and pH decreased, while total titratable acidity increased at 2.0 and 2.5% concentrations in the soursop, cowmilk, goatmilk yoghurt and cheese samples as storage period increased. The control counts after two weeks were 3.6x107, 8.7x107 and 1.7x106 cfu/mL while the extracts preserved the samples for eight weeks, after which total plate counts were 1.4x107, 5.3x105 and 0.8x106 cfu/mL for soursop, cowmilk and goatmilk yoghurts respectively. The rate of multiplication of yeast and mould counts were retarded in treated samples but conversely in control. There were no significant differences between the yoghurts made from soursop, cow milk and goat milk in terms of overall acceptability. However, overall acceptability of cheese from cowmilk was significantly (p<0.05) higher than others.
Mixture of aqeous extract of Aframomum danielli and Curcuma longa preserved refrigerated yoghurt and cheese for eight weeks. Both spices at 2.5% concentration performed best as preservatives.
