Although mothers' milk is the best food for babies, infant formula has become an alternative when breastfeeding is not possible or inadequate for babies. To design a proper formula for babies, understanding digestibility of macronutrients and their bio-accessibility in the gastrointestinal tract is essential. In vivo gastrointestinal studies on human infants are restricted by ethical constraint, cost issues, and intensive resource. However, in vitro models offer many advantages with low cost, easy sampling accessibility and no ethical issues. This article aims at reviewing the main aspects of the infant physiological gastrointestinal tract and providing an insight on recent in vitro research on infant formula.

9Low fat Cheddar cheese (LFC) with up to 91% fat reduction were prepared using four levels 10 of sodium alginate (alginate): 0.12 (LFCA1), 0.17 (LFCA2), 0.18 (LFCA3) and 0.23% (w/w) 11 (LFCA4). Control full fat cheese (CFFC) and control low fat cheese (CLFC) were used for 12 comparison. Physical characteristics, namely texture profile, microstructure, transverse 13 relaxation time (T 2 ) distribution (measured by low-field NMR) and color were analysed 14 periodically during ripening until 180 days. Texture profile analysis illustrated a significant 15 improvement in texture of alginate added LFC (P<0.05) as compared to CLFC. The textural 16 attributes of LFCA1 ripened for 30 days were comparable to CFFC ripened for 60 days and 17 beyond. A close resemblance in textural attributes between alginate added LFC and CFFC, 18 not previously reported when using other fat replacers, was observed. Scanning electron 19 micrograph (SEM) images revealed that alginate added LFCs had smoother surfaces as 20 compared to CFFC and CLFC, and the dense and compact protein matrix characteristic of 21 CLFC was not observed. Confocal laser scanning microscopy (CLSM) suggested that the fat 22 particle size, area and volume were affected in all LFCs due to their lower fat level and these 23 parameters increased during ripening in CFFC. NMR results revealed increase in higher 24 mobility water fraction in alginate added cheese compared to CFFC and CLFC. Hunter L, a 25 and b values for alginate added LFCs indicated that they were whiter than CLFC and less 26 yellowish than CFFC at the beginning of ripening; the color of some of the alginate added 27 LFCs was comparable to CFFC after 120 days of ripening. Overall, addition of alginate 28 significantly improved the textural, microstructural properties and color of LFCs, affirming 29 its potential as a promising texture modifier.30

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