| Abstract
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In freeze-drying, reported retentions of non-volatile dispersed phases are usually low. The objective of this work was to determine what factors limit retention, and to formulate an encapsulation system surpassing those limitations. O/W emulsions were prepared with cottonseed oil emulsified into aqueous carbohydrate solutions. Various emulsification methods and a variety of emulsifier types were tested. Maltose and maltodextrins matrices were used. The maltodextrins varied in DE, MW and Tg values. Processing conditions were varied, especially platen/chamber temperature during drying. Surface (unencapsulated) oil was determined gravimetrically by pentane extraction. Sonication and pressure homogenization (2 stage) were the best emulsification methods. Sonication with an aqueous solution of emulsifier, matrix carbohydrate added afterwards, gave much higher retention than with matrix carbohydrate present during sonication. At a platen temperature of usd\rm {-}2\sp\circ C,usd polymeric emulsifiers like Na caseinate, gelatins and hydroxypropyl methyl cellulose (HPMC) gave better retention than gum arabic, or the small molecule emulsifiers lecithin and Polysorbate 60(PS60). At usd\rm {-}2\sp\circ Cusd retention was poor. Retention was best at usd\rm {-}15\sp\circ C.usd A polymer film around droplets, or solid lipid droplets, improved retention. When Na caseinate was used as emulsifier, drying was done at a chamber temperature of usd\rm {-}15\sp\circ C,usd and the matrix was 30% maltose, retention of 80-99% was obtained, the best achieved. Retention was sometimes improved by diluting to 15-20% maltose. Water loss during drying was sometimes improved by dilution. Drying at usd\rm {-}15\sp\circ C,usd with caseinate as emulsifier, and maltodextrins as matrices gave best retentions up to 75-85%. Differences in retention with the different maltodextrins are presented. The positive effects of the maltodextrins were more evident from the appearance of the samples. These effects were not reflected in retention differences compared to maltose. The retentions reported here are much better than most retentions reported previously for the freeze drying of emulsions. Our results demonstrate that retention is improved by conditions which prevent surface oil formation, and which maintain adequate porosity for good drying. Further improvement in retention and quality during freeze-drying will probably require gaining control over the freezing process, so that porosity is minimized, while still being adequate for good drying.
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