Optimization of processing parameters for manufacture of flavored lassi from buffalo milk

Introduction

Take one of the fastest-growing categories in the Egyptian dairy segment -ready-to-drink flavored fermented milks -and look at what separates a product that wins retail shelf space from one that does not. The answer, repeatedly, comes down to three things: consistent flavor across the shelf life window, no visible phase separation, and an acceptable drift in acidity across two to three weeks [1,2] . For lassi made from buffalo milk, delivering on all three is trickier than for cow milk because buffalo milk carries 6.5 to 7.8 percent fat against 3.8 to 4.2 percent in cow milk, and its larger native fat globules (5 to 8 µm) cream out quickly unless properly homogenised [3] . Buffalo milk also carries higher casein and lower whey protein, which shifts the syneresis behaviour of the fermented curd. Research on flavored lassi processing has covered individual variables in isolation. Kumar and colleagues evaluated sugar levels in cow-milk lassi but did not homogenise [4] . Desai et al. compared flavor types using standardised buffalo milk but held pressure fixed at 1500 psi [5] . Rao's factorial research on homogenisation addressed cow milk only [6] . Khan and associates used response surface methodology for buffalo-milk lassi but limited the research to textureprofile responses [7] . A combined optimisation that cross-factors homogenisation pressure, sugar level and flavor for buffalo-milk lassi has not been published for the Egyptian context. The present research was framed around that gap, with three factors at three levels each giving a 27-cell factorial arrangement evaluated across sensory, rheological, microstructural and shelf-life endpoints.

Material and Methods

Material

The research was conducted at the Department of Dairy Science, Alexandria University of Agriculture, Alexandria, Egypt, between June 2022 and February 2023. Raw buffalo milk was sourced from the institutional dairy herd, consisting of Egyptian buffalo and Murrah crosses in mid-lactation. Milk was standardised to 4.5 percent fat and 8.8 percent solids-not-fat before each processing run. A defined lactic culture of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus (1:1 ratio, APRI-144 and APRI-74 respectively) was procured from the Animal Production Research Institute, Cairo. Food-grade flavor concentratescardamom oil (0.02% v/v), saffron extract (0.15% w/v) and rose attar (0.05% v/v) -and commercial sucrose were used for product formulation. Packaging was in 200 mL foodgrade HDPE bottles with induction-sealed caps.

Instrumentation and Safety Considerations

A two-stage APV Gaulin homogeniser (model LAB-60, 2500 psi maximum working pressure) was used for milk-fat reduction. Sensory assessment took place in a booth compliant with ES 4247:2012 at 21±1 °C. A Brookfield DV-II viscometer (SC4-21 spindle at 30 rpm, 20 °C) gave apparent viscosity; droplet size distribution was read on a Malvern Mastersizer 3000. A calibrated digital pH meter and hand-held refractometer covered acidity and sugar checks. Because the final product is chilled-stored rather than thermally processed after packing, microbial safety was tracked at every sampling point through standard plate count, yeast-and-mould count and coliform count following Egyptian Standards ES 1623 protocols. Packaging operations were conducted under laminar flow. A temperature logger verified cold-chain integrity (4 to 6 °C) through the 21-day shelf window.

Methods

A 3 × 3 × 3 factorial research was conducted with homogenisation pressure (1500, 2000, 2500 psi), sugar level (5, 7, 9%) and flavor (cardamom, saffron, rose) as factors, in three replications. Standardised milk was preheated to 62 °C for 30 minutes, cooled to 42 °C and inoculated with 2 percent starter culture. Fermentation proceeded to pH 4.4 over 5.5 to 6.0 hours. The curd was churned for 4 minutes, homogenised at the assigned pressure in two stages (75% primary, 25% secondary), blended with sugar syrup and flavor, bottled and cold-stored at 5±1 °C. Sampling was done on day 0, 7, 14 and 21. Sensory evaluation used a 9point hedonic scale with a trained panel of nine. Apparent viscosity, droplet size D [4,3] , pH, titratable acidity, syneresis (centrifugal method), standard plate count and yeast-mould count were measured. Response surface regression on MINITAB 19 identified the optimum; factorial ANOVA with Duncan's test at p<0.05 separated treatment means.

Results

All three factors and their two-way interactions significantly influenced sensory, rheological and microstructural responses. Homogenisation pressure emerged as the dominant factor for droplet size and viscosity, while sugar level controlled sweetness and overall acceptability in a curvilinear fashion. Flavor type influenced aroma and flavor-balance scores but had a smaller effect on physical stability parameters.

Comprehensive Interpretation

Response surface modelling placed the optimum at 2000 psi homogenisation pressure, 7 percent sugar and cardamom flavor, with a predicted overall acceptability of 8.58 and an observed value of 8.60. Composite desirability across all response variables was 0.893 on a 0-to-1 scale. Critically, every quality parameter stayed within commercial acceptance bands through day 14 of chilled storagesensory score above 7.4, syneresis below 6.2 percent, pH above 4.18, and yeast-mould count below 2.5 log cfu per millilitre. The shelf-life window effectively doubled relative to the un-homogenised control, which failed by day 7 on phase separation and sensory scores.

Discussion

The central finding is that 2000 psi two-stage homogenisation is the sweet spot for buffalo-milk lassienough to break fat globules below 2 µm and stabilise the phase system, but not so much that protein network damage raises syneresis. The optimum sensory score of 8.6 at day 0 and 7.4 at day 14 sits close to the 8.4 and 7.2 values reported by Khan et al. for their 1800 psi optimisation [7] , and comfortably above the 6.8 and 6.1 figures obtained by Desai and colleagues at 1500 psi [5] . Consumer preference trials across Egyptian markets have consistently ranked cardamom above saffron and rose for fermented dairy beverages [8] , and the present sensory data reinforce that pattern, with cardamom out-scoring saffron by 0.4 points and rose by 0.7 points. The research diverges from Rao's cow-milk optimisation [6] , which placed the best pressure at 2500 psi. Buffalo-milk casein forms a denser network after fermentation, and higher pressures shear this network enough to initiate syneresis earlier than in cow milk. The larger initial fat globule size of buffalo milk means that 2000 psi already achieves sub-2 µm droplets, and additional pressure pushes into the regime where beneficial dispersion tips into protein damage. The shelf-life extension is explained by the caseinstabilised droplet model: smaller droplets present more surface area for casein adsorption, creating a mechanically stronger matrix that resists creaming, holds flavor compounds in place, and buffers pH drift. Implications for mid-scale dairies are direct: a single-pass upgrade to 2000 psi two-stage homogenisation, coupled with a 7 percent sugar target and cardamom as default flavor, should deliver a reliable two-week chilled shelf life without additional stabilisers or preservatives. This matters because consumer demand for cleaner-label fermented beverages continues to grow [9] .

Conclusion

The main contribution of this research is a validated threefactor optimisation for flavored lassi made from buffalo milk, built on a 27-cell factorial arrangement evaluated across sensory, rheological, microstructural and microbial endpoints through a 21-day chilled shelf-life window.

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