Review Isomerization oflactose and lactulose production: review Mohammed Aider a,b, * and Damien de Halleux c a Department of Food Sciences and Technology, Laval University, Quebec G1K 7P4, Canada (Department ofFood Sciences and Technology, Universite ´ Laval, Pavillon Comtois, STA, Que ´ bec G1K 7P4, Canada; e-mail: [email protected]) b Institut National des Nutraceutiques et des Aliments Fonctionnels (INAF), Laval University, Quebec G1K 7P4, Canada; e-mail: [email protected]c Department of Food Engineering, Universite ´ Laval, Pavillon Comtois, Que ´ bec G1K 7P4, Canada Lactulose is widely used in pharmaceutical, nutraceuticals and foo d ind ust rie s bec ause of its ben efic ial eff ects on human health. Technology of lactulose production is mainly based on the isomerization reaction of lactose in alkaline media. However, information available on this subject is very varied. This study is a summary of the principal techniques used for lactulose production in order to gather maximum information in on e manu sc ri pt for a be tt er comp rehension of the techn ologi cal char acteristics and specifi cities of lactul ose synthesis. Introduction Significant part of the world population suffers from gas- troint estinal disease s of various types. Several of these dis- eases are caused by pathogenic bacteria which invade the human intestine. A few days after the birth, the human in- tes tine is col oni zed mai nly by bifidob act eri a whi ch pla y a very important role in the maintenance of a good health. By cha ngin g the nut rit ion regime and chi ldr en passage from mother’s milk nutrition to ordinary food regime, the pa thogenic bacteria which infiltra ted into the human intestine cause diseases of various types. In order to solve this health problem, food industry and in particular dairy tec hno logy has de vel ope d dai ry bio -pro duc ts enr iched with probiotics like lactobacillus ( Lactobacillus acidophi- lus, Lacto bacillu s casei , Lactobac illus bulga ricus , et c. ) and bifidobacte ria ( Bifidobacteria bifidum, Bifidobacteria longum, Bifidobacteria infantilus, Bifidobacteria adolescen- tis) (Clark & Ma rti n, 1994; Donkor , Nilmi ni , Stol ic, Vasil je vic, & Shah, in pr ess; Ka tz, 2006; Ni nonuevo et al., 2007; Olguin, et al., 2005; Wainwright, 2006). How- ever, because of various reasons, this solution did not solve the problem. These reasons could be resumed by the fol- lowing: a great loss of bacterial cells during the production process of different dairy products noticed by several re- searchers, a considerable reduction of the total of bacterial number due to storage at pH values lower than 5.5 as well as because of the strong acid medium in the stomach (pH y 1.5) and the negative effect of bile salts (Chou & Hou, 2000; Lankaputhra & Shah, 1995; Lian, Hsiao, & Chou, 2002). An al terna ti ve to the resolutio n of this pr oblem con sis ts in an int ern al sti mula tion of the bifidobact eri a wh ic h ar e al re ady pr esent in the intest ine ( Bouhniket al., 1990; Del zenne, 200 3; Gib son, Bea tty, Wang, & Cummings, 1995; Mizota, T amura, Tomi ta, & Okono gi, 1987). This method consists in using bifidogenic functional food ingredients, known under general name of prebiotics (Kap lan & Hut kins, 200 0; Mar tea u & Bou tron-Ruault, 2002; Roberfroid, 2002; Sa ar ela, Ha lla maa , Matt ila- Sandholm, & Matto, 2003; Ziemer & Gibson, 1998). These bifidogenic ingredients stimulate the growth of bifidobacte- ria (Tamura, Mizota, Shimamura, & Tomita, 1993). Lactu- lose is one of these ingr edient s ( Ala nde r et al. , 200 1; Ballo ngue, Schumann , & Quign on, 1997; Saarela et al., 2003). Lac tulose is a syn thetic dis acc hari de obt ain ed by an isomer iza ti on reac ti on of lact ose whose mi lk and la ct ose rum ar e ve ry ric h ( Zokaee, Kag hazchi, Zar e, & Soleimani, 2002). The average lactose content in milk or mi lk whey is appr oximat ely 4. 5% ( Lindmark-Mansson, Fonden, & Pettersson, 2003). Several studies showed the effe ctive ness of lactul ose to stimula te the growth of bifido - bacteria (Martin, 1996; Mizota, 1996; Sako, Matsumoto, & T anaka, 1999; Shin, Le e, Petska , & Ustunol, 2000; Strohmaier, 1998). Moreover, lactulose is widely used in pharmaceutical industry as an effective drug against differ- ent diseases like acute and chronic constipation (Mizota, Tamura, Tomita, & Okonogi, 1987; Tamura et al., 1993). * Correspo nding author . 0924-2244/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2007.03.005 Trends in Food Science & Technology 18 (2007) 356 e364
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Review
Isomerization of
lactose and lactulose
production: review
Mohammed Aidera,b,* and
Damien de Halleuxc
aDepartment of Food Sciences and Technology, LavalUniversity, Quebec G1K 7P4, Canada (Department of
in U.S. Patent No 4536221 (1985), the use of magnesium
hydroxide mixed with sodium hydrosulphide in lactose so-
lution of 60e70% concentration was reported. The catalyst
concentration in this case was 0.05e0.2% and the temper-
ature used was 90e100 S.
Isomerization of lactose by aluminates and borates Using amphoteric electrolytes such aluminium hydrox-
ide or boric acid, total isomerization yield of lactose into
lactulose could reach 70e80% (European Patent
0320670, 1990; Mendicino, 1960; U.S. Patent 4273922,
1981). In these cases, the catalyst must be added at a rate
of 0.5e4 M per mole of lactose as reported in the US patent
No 4957564. In U.S. Patent No 3546206 (1970), it was re-
ported that catalyst (aluminate) was added to lactose solu-
tion. Thereafter, the mixture was heated and thermostated
a certain time and then the catalyst was removed fromthe medium using crystallization by cooling. The pH was
readjusted with HCl or aluminium hydroxide, dependently
on the case. At the end of the process, it was recommended
to isolate lactulose using methanol. Carrobi and Innocenti
(1990) proposed using of membrane to remove catalyst af-
ter isomerization. Following this work, patent was depos-
ited (U.S. Patent No 4957564, 1990). In these patents, it
was reported that 25e50% lactose solution was used. The
catalyst (sodium aluminate) was added in the form of
35e45% concentration solution. The ratio aluminate/lac-
tose was 0.3/1 up to 1/1, dependently on lactose concentra-
tion. Isomerization was carried out under a temperature of
50e
70 C during 30e
60 min. At the end of the reactiontime, solution was neutralized with 3e4 N sulphuric acid
to keep pH in the range of 4.5e8.0. Aluminium hydroxide
suspension was formed and then removed from the medium
by centrifugation followed by membrane treatment. Other
authors reported the use of sodium tetraborate, sodium hy-
droxide or triethylamine mixed with boric acid as catalyst
(Hicks, Raupp, & Smith, 1984; Mizota et al ., 1987). Crys-
tallization, pasteurization and purification operations by ion
exchange resins were necessary.
Isomerization of lactose by alkaline-substituted sepiolites De la Fuente, Juarez, de Rafael, Villamiel, and Olano
(1999) reported that strong base catalysts, prepared by
substituting a part of the Mg2þ located at the borders of
the channels of sepiolite with alkaline ions (Liþ, Naþ, K þ
and Csþ), were investigated as catalysts for the isomeriza-
tion of lactose to lactulose and epilactose. The activities ex-
hibited by alkaline-exchanged sepiolites were significantly
higher than that of natural sepiolite. The influence of
temperature, time of the reaction and catalyst loading
were also evaluated. A 20% conversion was obtained at
90 C at a catalyst loading of 15 g/l. At the other hand,
Villamiel, Corzo, Foda, Montes, and Olano (2002) reported
that alkaline-substituted (Naþ, K þ) sepiolites were used as
catalysts for the formation of lactulose in milk permeate.
Besides lactose and lactulose, other carbohydrates, such
as galactose and epilactose, produced in side reactions,
were determined. The effect of different washing cycles
of sepiolite on the isomerization of lactose and the ex-change of cations with the permeate was also investigated.
In general, the activity of the sodium sepiolite was higher
than that of potassium form. Twenty per cent of lactulose
formation (1000 mg/100 ml), with respect to the initial lac-
tose, was obtained after 150 min of reaction, using sodium
sepiolite washed during 10 cycles. Under these conditions,
25% of lactose degradation was detected, whereas small
amounts of epilactose and galactose were formed. The ex-
change of Naþ between sepiolite and permeate decreased
considerably with the number of washing cycles. The pres-
ent work shows an appropriate method for obtaining lactu-
lose in milk permeate with acceptable yields and withoutcomplicated purification steps.
Lactulose production by ion exchange resins Production of lactulose in a form of concentrated solu-
tions or powder for use as additive in functional food is
more and more of topicality. This type of product must
be at the same time safe and easy to produce, whether for
environment or human consumption. Based on this concept,
several works were carried out during the 10 last years in
order to find effective technologies for lactose isomeriza-
tion into lactulose without use of reactive agents. As it
was mentioned above, lactulose production requires useof chemicals (hydroxide, borates, aluminates, etc.) and
purification procedures by ion exchange resins.
In the Russian Patent No 2101358 (1998), anion ex-
change resins were used to intensify process isomerization
of lactose into lactulose by exploiting OH ions exchange
between solution in reaction and resins and to simplify lac-
tulose production process by using the same resins for de-
mineralization of the end product. The advantages of this
process are
There is no need to add catalyst for isomerization
process;
Demineralization stage is not used; No additional operation to purify the end product from
dyes;
He process is more profitable in comparison with tradi-
tional methods;
Lactulose produces by this technology could be used in
functional food for children, and in specialized food into
which bifidobacteria are introduced (Hramtsov et al.,
2004).
Concluding remarksLactulose production is a complex process, which is af-
fected by several operation and technological conditions.
362 M. Aider, D.de Halleux / Trends in Food Science & Technology 18 (2007) 356 e364
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Most of the changes incurred to the lactulose by heating are
disadvantageous to quality of the final product. However,
degradations can be minimized by appropriate design of
the isomerization process, type of catalyst used and
lactose quality. Designing process of lactose isomeri-
zation into lactulose must be done in a comprehensiveway considering pre-isomerization, isomerization and post-
isomerization processes. Isomerization of lactose into
lactulose must be preceded by adequately chosen raw
material yields with expected quality and optimal lactose/
catalyst ratio. That quality can be maintained during lactu-
lose isolation by application of appropriate post-processing
parameters. Because of complex influence on the product
and many technological variables, which can be controlled
during processing, isomerization is a versatile way to treat-
lactose, which is an abundant product of cheese processing.
A thorough knowledge of pros and cons of the isomerization
process is needed in order to design optimal technologicalprocess for lactose isomerization into lactulose with a mini-
mum of by-products and to obtain final product of desired
quality for a variety of use.
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