Survival of Lipase during Manufacture of Nonfat Dry Milk

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Extracellular lipases from several strains of Pseudomonas fluorescens were active against milk fat. The activity of P. fluorescens strain B52 lipase in reconstituted NDM using β-naphthyl caprylate as substrate was 70% of that found with skim milk; however, hydration of the NDM at 4°C for 12h resulted in 85% recovery of activity. As little as .0025% (vol/vol) of P. fluorescens spent media was detected in reconstituted skim milk powder using β-naphthyl caprylate. The process of freeze-drying or spray-drying without heating had little effect on either native or P. fluorescens B52 lipase. The bacterial lipase activity was reduced by 12 to 21% and 55 to 59% in NDM treated with low heat (72°C/16s) and high heat (110°C/2min), respectively, while the native lipases were completely inhibited by these treatments. Both native and bacterial enzymes were stable when stored in NDM for extended periods at 20°C. In a limited study of commercial NDM samples, microbial lipase was not detected, suggesting that the quality of the raw milk was sufficiently high to restrict the presence of heat-stable lipolytic enzymes.