Lactulose: Significance in Milk and Milk Products
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Int.J.Curr.Microbiol.App.Sci (2016) 5(11): 721-732 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 5 Number 11 (2016) pp. 721-732 Journal homepage: http://www.ijcmas.com Review Article http://dx.doi.org/10.20546/ijcmas.2016.511.083 Lactulose: Significance in Milk and Milk Products Sonali L. Parekh*, Smitha Balakrishnan, Subrota Hati and K. D. Aparnathi Department of Dairy Chemistry, SMC College of Dairy Science, Anand Agricultural University, Anand-388110, India *Corresponding author ABSTRACT K e yw or ds Many kinds of lactose derivatives can be obtained using various methods, including epimerization, oxidation and reduction. Lactulose is not only utilized as an Epimer, indicator substance for milk heat treatment but it also represents one of the most Isomerization, Prebiotic, valuable lactose derivatives with therapeutical applications dating back to the Endotoxemia. middle of the last century. Lactulose is a non-caloric, synthetic disaccharide formed from one molecule each of fructose and galactose. Technologically, lactulose can be produced by the isomerization of lactose molecule in which a new ketose sugar Article Info from aldose by regrouping the glucose residue to the fructose molecule. It is widely Accepted: used in pharmaceutical and food industries because of its beneficial effects on 26 October 2016 human health. In particular, lactulose, galactooligosaccharide and lactitol are used Available Online: in foodstuffs and pharmaceuticals, and new lactose derivatives such as epilactose 10 November 2016 and tagatose have also recently received attention. Introduction Chemistry and Properties of Lactulose Lactose, a unique disaccharide, occurring exclusively in the mammalian milk plays an Lactulose (4-O-β-D-Galactopyranosyl-D- important role in nutrition. Most of the fructofuranose), the isomerized lactose, is a lactose that is manufactured on an industrial disaccharide consisting of galactose and scale is produced from whey derived from fructose with a molecular weight 342. It the production of cheese, casein or paneer belongs to the few carbohydrates other than using crystallization and purification lactose that play an important role in the technologies. Lactose can be converted to dairy fields (Gaenzle et al., 2008). Although various derivatives like lactitol, lactobionic Lactulose was first systhesized in 1929 acid, galacto-oligosaccharide, epilactose (Montgomery and Hudson, 1930) etc., using laboratory or industrial processes. physically, its significance was not They are widely used in food and in recognized until 1957 when Petuely pharmaceutical fields due to their special discovered that it act as a growth factor for characteristics. Lactulose is a derivative of Bifidobacteria (Petuely, 1957). lactose obtained by Isomerization of glucose It is more soluble in water than lactose and moiety of lactose to fructose (Claeys et al., about half as sweet as sucrose and does not 2001). crystallize easily even in concentrated 721 Int.J.Curr.Microbiol.App.Sci (2016) 5(11): 721-732 solutions. Lactulose is much less stable in Production of lactulos Chemical methods solution than lactose and may subsequently degrade via process of β-elimination to give Industrial production of lactulose is galactose, tagatose and saccharinic acids and exclusively carried out by chemical other low molecular weight products (Olano isomerization of lactose via the Lobry de and Martinez-Castro, 1981). Subsequently, Bruyn-Alberda van Ekenstein (LA) lactulose may epimerize via a 2,3-enediol to rearrangement. Three different methods form epilactose (4-O-β-D-galactopyranosyl- namely alkalising catalysts, complexing D-mannose).It reduces Fehling's solution on agents and ion-mediated process are heating. employed for lactulose production by chemical methods. As per Speck (1958) two main pathways should exist since the pH range of milk Alkalising catalysts systems permits the possibilities of transformation in two ways. The first path is Alkaline catalysts like triethylamine, sodium theLobry de Bruyn-Alberda van Ekenstein hydroxide, magnesium oxide and sulfites, (LA) transformation. This is in essence an provoking a pH of 10-12 in the reaction alkaline isomerization. The second theory of mixture, have been successfully employed the mechanism of lactulose formation for the isomerization of lactose assumes the formation of lactosylamine (Montgomery and Hudson, 1930). A new which undergoes Amadori rearrangement to group of catalysts was introduced with lactulose by hydrolytic degradation. calcium carbonate-based by-products like egg and oyster shells (Montilla et al., 2004; Formation in Milk during Heat Villamiel et al., 2002). Treatment Complexing agents Temperatures above 100°C as applied in the production of sterilized and UHT milk The employed catalysts are borate and enhanced product stability, but also induce aluminate which form an insoluble complex several chemical reactions of milk with ketose sugars like lactulose under components, such as the isomerization of alkaline conditions (Hicks and Parrish, lactose into lactulose. In the case of 1980; Kozempel and Kurantz, 1994). lactulose formation, the glucosemoiety of Zokaee et al. (2002) reported that under lactose is isomerized into its keto-analogue similar reaction conditions Ylactu/lacto was fructose, a process which is favoured by heat about 80% for borate, whereas with and alkaline conditions. Observed lactulose aluminate less lactulose was formed concentrations vary between 0.3 g/l for UHT (Ylactu/lacto ¼ 70%) and its degradation was milk and 1.6 g/l for sterilized milk increased (Hicks et al., 1984). (Mendoza et al., 2005). Ion-mediated processes Increasing the content of lactulose in milk by extending heating time or temperature is Alkalisation of whey was achieved by not possible due to a heat-induced drop of circulation over strong ion exchange resins pH and a simultaneous thermal degradation activated with hydroxide ions. The exchange of lactulose. of ions like chloride and the subsequent release of hydroxide ions from the resin 722 Int.J.Curr.Microbiol.App.Sci (2016) 5(11): 721-732 increased the pH of whey and induced the (Hua et al., 2010). Mayer et al., (2010) LA-transformation of lactose into lactulose developed a continuous enzymatic process (Khramtcov et al., 2004). Ion-mediated for the production of lactulose through processes have not been established in transgalactosylation using free and industrial processes yet. Evdokimov and immobilized β-glycosidase from Pyrococcus Alieva (2004) suggested using the alkaline furiosus. fraction of electrochemically activated water or lactose solutions obtained by electro- Using whole cells membranous methods for the production of lactulose. Whole cells used as biocatalyst for the production of lactulose often causes very Enzymatic Method low reaction rates due to permeability barrier of the cell envelope for substrates Enzymatic synthesis of lactulose is and products. The permeabilized commonly carried out with classes of Kluyveromyces marxianus cells as a source enzyme β-galactosidase and glycosidase. β- of β-D-galactosidase were used to overcome galactosidase is a well-known biocatalyst for this problem. Ethanol permeabilization of transgalactosylation reaction and for the yeast cells has been shown to be an synthesis of lactose based derivatives economical, easy, convenient and safe (Lee including galacto-oligosaccharides (Panesar et al., 2004). et al., 2006; 2010). Extraction and Purification of Lactulose Using free enzymes During lactulose production, the reaction Mayer et al.(2004)reported the production of mixture is generally not pure, and usually lactulose by enzymatic transgalactosylation contains appreciable quantities of other from lactose to fructose by using β- substances such as lactose, glucose, galactosidase from Aspergillus oryzae and galactose, epilactose etc. The recovery of the hyperthermostable β- glycosidase from lactulose during downstream processing has Pyrococcus furiosus.Further, gene encoding been found to be an important reaction a thermostable β-galactosidase from because the amount of purified lactose was Sulfolobus solfataricus has been cloned and affected by both physical and chemical expressed in Escherichia coli for lactulose treatments. A strong acidification of production (Kim et al., 2006).Enzymatic obtained solution has been carried out at synthesis of lactulose from whey permeate temperature in order to release lactulose and was affected by β-galactosidase preparation, to induce precipitation of borate as boric substrate concentration and by theratio of acid and sodium aluminate as gel like lactose and fructose (Adamczak et al.,2009). aluminium hydroxide (Kozempel et al., 1995). Moreover, separation steps have been Using immobilized enzymes evolved for the removal of borate by the crystallization of boric acid of 50% in a Lactulose has also been successfully solution with 20% (w/w) carbohydrates and synthesized by dual enzymatic consisting of 15% (w/w) borate (Kozempel et al., 1995). immobilized lactase and immobilized But, in case of heterogeneous catalysts (like glucose isomerase. Immobilized lactase is powdered egg shells), centrifugation method prepared by cross-linking the free lactase has been used for recovery of lactulose and - into Fe3O4 chitosan magnetic microspheres the obtained sugar solution has been 723 Int.J.Curr.Microbiol.App.Sci (2016) 5(11): 721-732 decolourized using activated carbon without Physiological Effects of Lactulose decreasing