PhD

The study entitled “Standardisation and quality evaluation of banana based probiotic fermented food mixtures” was undertaken with the objective to standardise indigenous food mixtures based on banana flour with probiotic fermentation with Lactobacillus acidophilus and to evaluate the nutritional factors, organoleptic qualities and storage stability of the food mixtures.

Probiotic characteristics like acid and bile tolerance and antimicrobial activity of L.acidophilus MTCC 447 showed an acid tolerance ranging from pH 2.0 - 9.0 , a bile tolerance of three per cent and antagonistic activity against enteropathogens viz Salmonella enteritidis, E.coli, Bacillus cereus and Staphylococcus aureus.

The foods selected for developing the probiotically fermented food mixtures were banana (Nendran), defatted soya flour, green gram flour, ripe mango, papaya and tomato. From the 56 combinations tried, 14 fermented food mixtures with L. acidophilus MTCC 447 were selected statistically by applying Kendall’s coefficient of concordance.

All the 14 selected food mixtures contained 60-70 per cent banana flour, 20 per cent defatted soy flour / green gram flour and 10-20 per cent fruit pulps.

For all the treatments variables of fermentation were optimised as 25g of the food mixture (substrate), pH 4.5, inoculum 300µl (119 x 106 cfu /ml), temperature of incubation 37 ºC and time of incubation 24 hours.

All the fermented foods along with unfermented controls were freeze dried. Constituents like titrable acidity (2.59 g lactic acid / 100g), protein (7.82g/100g), iron (6.48mg/100g), thiamine (0.0726 mg/100g) and riboflavin (0.535 mg/100g) were significantly high in fermented food mixtures. in vitro digestibility of starch (82.109 per cent) and protein (85.85 per cent) were also significantly high in fermented food mixtures. Total viable count of L. acidophilus ranged from 9.13 to 9.46 log cfu/g. Mean score of overall acceptability of fermented products were between 7.9-8.0 in a 9 point hedonic scale.

From 14 fermented food mixtures, six fermented food mixtures were statistically selected considering all the quality aspects by geometric mean score. The selected food mixtures T1, T2, T3, T7, T8 and T9 along with their respective controls were packed in metallised poly ester / poly ethylene laminate pouches and kept for storage studies under ambient conditions for a period of six months.

From the six fermented food mixtures with maximum shelf life qualities, three fermented food mixtures were statistically selected by applying geometric mean score. The treatments with maximum geometric mean score were T1 (70 per cent banana flour, 20 per cent defatted soy flour, 10 per cent mango), T3 (60 per cent banana flour, 20 per cent defatted soy flour, and 10 per cent tomato pulp) and T8 (60 per cent banana flour, 20 per cent defatted soy flour,10 per cent mango and 10 per cent tomato pulp).In all the selected three treatments, viable count of L.acidophilus ranged from 8.84 to 9.12 log cfu/g after six months of storage. This viable count was within the desired level of probiotic organisms recommended

Substrate composition was modified by adding sucrose, sorbitol, wheat bran and skimmed milk powder to T1, T3 and T8.The level of these four ingredients were standardised as five per cent in T3, with maximum viable counts of L.acidophilus ranging from 9.45 to 9.54 log cfu/g. Thus five treatments (T3 + sucrose 5 %, T3 + 5% sorbitol, T3 + 5% wheat bran and T3 + 5 % skimmed milk powder) was subjected to quality evaluation and shelf life studies.

After modifying the substrate, food mixture T3S (with added sucrose at 5 per cent level) showed high acceptability and an increase in the viable count of L.acidophilus after storage, when compared to T3 (control).T3SB (with added sorbitol at 5 per cent level) was comparable to that of T3 (control) in any aspect. T3W (with added wheat bran at 5 per cent level) was also comparable to T3 (control) but with an increase in the total viable count .T3SK (with added skimmed milk powder at 5 per cent level) showed an increase in all the nutrients, acceptability and viable counts. Hence, these four food mixtures (T3S. T3SB, T3 W and T3 SK) can also be recommended as good probiotic food mixtures.

The viable count of L. acidophilus in the developed probiotic food mixtures at the expiry period (after six months of storage) ranged between 95 to 210 x 107 cfu/g and in five grams the viability ranged between 475 to 1040 x 107 cfu. This was within the recommended level of the probiotic organism to assure health benefits. Since the fermented food mixtures were slightly acidic in taste, it can be used with acidic foods like buttermilk, fruit juices etc to enhance their acceptability. The cost of the developed food mixtures ranged between Rs 530 to Rs 550 for 400 grams.