Method for preparing a liquid oat base and products prepared by the method

Abstract

In a method of preparing a liquid oat base a material comprising oat bran is suspended in an aqueous media and contacted with -amylase, -amylase, -glucanase, and xylanase to raise the concentration of soluble arabinoxylan by a factor of 5 or more. Also disclosed is a liquid oat base obtainable by the method; a powderous oat base obtained by drying the liquid oat base; uses of the liquid and powderous oat bases and food products comprising them. A powderous composition for use in preparing liquid oat base comprises oat bran, -amylase, -amylase, -glucanase, and xylanase.

Claims

1. A method of preparing a liquid oat base for use in the manufacture of food for human consumption, comprising: (a) providing an oat bran material including from 1% to 50% by weight of -glucan; (b) suspending the oat bran material in an aqueous media, to form an aqueous suspension; (c) contacting, in no particular order, the aqueous suspension with a mixture of enzymes consisting of -amylase, -amylase, -glucanase, and xylanase for a period of at least about five minutes to raise the concentration of soluble arabinoxylan in the suspension by a factor of 5 or more to provide a liquid oat base; (d) homogenizing the liquid oat base of step (c) in a first homogenization step at a pressure of at least about 150 bar to provide homogenized liquid oat base; (e) optionally destroying enzymatic activity in the homogenized liquid oat base of step (d) to provide enzymatically inactive liquid oat base; and (f) optionally aseptically packaging the homogenized liquid oat base of step (d) or the enzymatically inactive liquid oat base of step (e) in a container; whereby the resulting liquid oat base contains oat bran particles which have an average particle size of at least 50 m.

2. The method of claim 1, wherein step (c) further comprises contacting the aqueous suspension of step (b) first with the -amylase, -amylase, and -glucanase to partially hydrolyze starch and -glucan, then with the xylanase to raise the concentration of soluble arabinoxylan in the suspension by a factor of 5 or more to provide a liquid oat base.

3. The method of claim 1, wherein the temperature for the -amylase, -amylase, and -glucanase contact is from 30 C. to 70 C.

4. The method of claim 1, wherein the temperature for the xylanase contact is from 40 C. to 70 C.

5. The method of claim 1, wherein the oat bran material is selected from the group consisting of oat bran, whole groat meal (whole meal), rolled oats groats and oat endosperm.

6. The method of claim 1, wherein the xylanase is an endo-1,4--xylanase.

7. The method of claim 1, wherein 80% or more of -glucan dissolved in the aqueous suspension is degraded by -glucanase to -glucan of a molecular weight ranging from 20,000 D to 400,000 D.

8. The method of claim 1, wherein the aqueous suspension is water.

9. A method of preparing a liquid oat base for use in the manufacture of food for human consumption, comprising: (a) providing a powderous composition consisting of oat bran material, -amylase, -amylase, -glucanase, and xylanase; (b) suspending the powderous composition in an aqueous media to form an aqueous suspension; (c) raising the temperature of the aqueous suspension from 40 C. to 70 C. for a time sufficient to degrade starch, -glucan, and xylan to form liquid oat base; wherein said -amylase, -amylase, -glucanase, and xylanase are allowed to act for at least about five minutes; (d) homogenizing the liquid oat base of step (c) in a first homogenization step at a pressure of at least about 150 bar to provide homogenized liquid oat base; (e) optionally destroying enzymatic activity in the homogenized liquid oat base of step (d) to provide enzymatically inactive liquid oat base; and (f) optionally aseptically packaging in a container the homogenized liquid oat base of step (d) or the enzymatically inactive liquid oat base of step (e); wherein the resulting liquid oat base contains oat bran particles which have an average particle size of at least 50 m.

10. The method of claim 9, wherein the media suspension is water.

11. The method of claim 1, wherein the homogenizing the liquid oat base of the step (c) is carried out using a two-step homogenizer wherein a first homogenization step is carried out at a pressure of at least about 150 bar and a second homogenization step is carried out at a pressure of at least about 30 bar.

12. The method of claim 9, wherein the homogenizing the liquid oat base of the step (c) is carried out using a two-step homogenizer wherein a first homogenization step is carried out at a pressure of at least about 150 bar and a second homogenization step is carried out at a pressure of at least about 30 bar.

13. The method of claim 1, wherein the oat bran particles have an average particle size of between 50 m and 1000 m.

14. The method of claim 1, where in the oat bran particles have an average particle size of between 140 m and 225 m.

15. The method of claim 9, wherein the oat bran particles have an average particle size of between 50 m and 1000 m.

16. The method of claim 9, where in the oat bran particles have an average particle size of between 140 m and 225 m.

17. The method of claim 1, wherein the oat bran material has a first total particle content and the homogenized liquid oat base has a second total particle content, wherein the first total particle content is equal to the second total particle content.

18. The method of claim 9, wherein the oat bran material has a first total particle content and the homogenized liquid oat base has a second total particle content, wherein the first total particle content is equal to the second total particle content.

19. The method of claim 1 wherein the treatment time is between five minutes and thirty minutes.

Description

SHORT DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a graph illustrating the effect of high pressure homogenization on liquid oat bran base of the invention containing all fiber present in the starting material and on a prior art decanted oat bran base from which such insoluble fiber has been removed by decantation;

(2) FIG. 2 is a graph illustrating the effect of high pressure homogenization on whole oat liquid oat base of the invention and on a prior art decanted oat bran base from which such insoluble fiber has been removed by decantation;

(3) FIG. 3 is a graph illustrating the particle size distribution of homogenized and not homogenized oat bran base of the invention as well as of a prior art control.

DESCRIPTION OF PREFERRED EMBODIMENTS

Materials and Methods

(4) Oat raw material. Oat bran, whole groat meal (whole meal), rolled oats groats and oat endosperm flour containing from 1% by weight to 50% by weight of -glucan, about from 8% by weight to 26% by weight of total dietary fiber, from 10% by weight to 22% by weight of protein and from 5% by weight to 15% by weight of fat.

(5) Endo (1-4)-xylanase. Xylanase Pentopan Mono BG was procured from Novozymes A/S, Denmark. By analysis it was established that the enzyme did not possess -glucanase activity. The enzyme (UB No. 3.2.1.8; CAS 9025-57-4) is produced by heterogeneous expression of Thermocytes lanuginosus in Aspergillus oryzae. It is a GH-11 family xylanase with a reported activity of from 2500 XU/W-g to >60000 XU/W-g at 40 C.

(6) Determination of -glucanase activity. The assay was performed using -glucazyme tablets from Megazyme International Ireland Ltd. by following the procedure provided by the supplier. The tablets were added to the enzyme solution in sodium acetate buffer (25 mM, pH 4.5) at 40 C. and the solution kept at this temperature for 10 min. The reaction was stopped by adding 6 ml of Trizma buffer (2% w/w, pH 8.5). Samples for analysis were centrifuged for 10 min at 2250 rpm. The absorbance of the supernatant was read at 590 nm.

(7) State-of-the-art liquid oat base (oat drink). A state-of-the-art oat base drink was prepared by adding dry commercial preparations of -amylase and -amylase in amounts sufficient to degrade the starch to maltose and maltodextrin. The drink was used as a starting material in experiments carried out for reasons of comparison.

(8) Liquid oat base of the invention. In addition to the use of -amylase and -amylase in the preparation of the liquid oat base of the invention -glucanase is used for degrading most or at least 75% by weight and even more than 80% by weight or 90% by weight of water soluble -glucan of the starting material, which has a molecular weight of about 1,000,000 D to about 2,000,000 D, to water soluble -glucan having a molecular weight of from about 20,000 D, in particular from about 50,000 D to about 400,000 D. The suspension of the starting material contained about 10% by weight of material rich in oat bran in water of about 60 C. After incubation for 1 h under stirring at this temperature the so produced liquid oat bran base had a pH of 6.4-6.6 and a viscosity of about 25 cP to 250 cP at 22 C. If desired, the process can be modified to obtain a product of higher or lower viscosity. This oat bran base of the invention was used in the following experiments.

(9) Estimation of soluble arabinoxylan release. The content of soluble arabinoxylan was determined according to the phloroglucinol method of Rose and Inglett, J Food Anal Meth 2; 1 (2010) 66-72. A 200 l aliquot of the oat suspension supernatant was mixed with 1 ml of reagent. The reagent consists of glacial acetic acid, concentrated hydrochloric acid, 20% (w/v) phloroglucinol in ethanol, and 1.75% (w/v) glucose in a proportion of 110:2:5:1. Samples were incubated at 100 C. for 25 min. After cooling to room temperature the absorbance was read at 552 nm and 510 nm. Quantification of the content of soluble arabinoxylan was obtained relating the measured absorbance to that of a calibration curve constructed by using D(+)xylose. The results are expressed as mM of xylose equivalents (XE).

(10) Determination of -glucan content. The method was developed using the Mixed-Linkage -glucan assay kit from Megazyme International Ireland Ltd. The procedure described by the supplier was slightly modified. One gram of oat bran based drink, 200 l of ethanol (50% v/v) and 4 ml of phosphate buffer (20 mM, pH 6.5) was added to each test tube. The tubes were vortex mixed and placed in boiling water for 2 min, then transferred to a water bath at 50 C. and kept there for 5 minutes. After adding 200 l of an aqueous solution of lichenase enzyme (10 U) to each test tube the samples were stored in the water bath for 1 h. Sodium acetate buffer (5 ml, 200 mM, pH 4) was added to each tube. The tubes were centrifuged at 1000 rpm for 15 min. One hundred L of the supernatant were mixed with 100 l of the -glucosidase enzyme (0.2 U) solution. A blank was prepared for each sample (no addition of -glucosidase; addition of 100 l of sodium acetate buffer (50 mM, pH 4)). Samples were incubated in a water bath at 50 C. for 15 min. A glucose standard was also analyzed. Three ml of GODOP reagent (potassium phosphate buffer (1 mM, pH 7.4), p-hydroxybenzoic acid (0.22 M) and sodium azide (0.4% w/w) was added to each tube. The tubes were then incubated for further 20 min at 50 C. The absorbance was read at 510 nm within 1 h.

(11) SDS-PAGE Gel Electrophoresis. To establish whether protein extracted after application of the enzyme differ from original protein a gel electrophoresis was performed at three different xylanase concentrations. It was shown that xylanase treatment does not affect the molecular weight distribution nor the composition of the proteins.

(12) Particle size measurement. Particle size measurement was performed by laser beam diffraction using a Mastersizer 2000, Hydro 2000SM instrument (Malvern Instruments, Worcestershire, UK). The particle size distribution recorded by this technique is volume based and reported in a graph showing the volume percentage of particles of a given size. The particle size determination is based on the assumption that the particles are spherical and homogeneous and that the optical properties of the medium are known. For particles of same kind, such as in the present context, the method is believed to render reliable results.

(13) EXAMPLE 1. -Glucan content of oat bran base of the invention in relation to amount of xylanase used for its production. The state-of-the-art oat bran based drink described above was incubated at 40 C. for 15 min with different amounts of xylanase. The product was analyzed for -glucan concentration. The results are shown in Table 1.

(14) TABLE-US-00001 TABLE 1 -Glucan content of oat bran base samples treated with different amounts of xylanase at 40 C. for 15 min Xylanase FXU/100 g OBF (Oat Bran) -glucan (% by weight) 0 1.3 100 1.4 1000 1.5 2000 1.4

(15) EXAMPLE 2. Physical stability of the improved liquid oat base of the invention. Physical stability was determined by measuring phase separation upon storing in a glass vial a sample of the improved liquid oat base for a given period of time at a selected temperature. During storage an upper clear liquid phase appeared. It increased in height until a stable end point state was reached at which the height of the lower particulate phase remained stable. Physical stability index I.sub.phs at time t.sub.ts is conveniently expressed as 100 the ratio of upper phase height at t.sub.s to upper phase height at end point (storage for indefinite period) at which sedimentation equilibrium has been reached.

(16) A decreased separation rate is indicative of improved physical stability. Homogenized samples of the aqueous oat base of the invention and the prior art aqueous oat base not treated with xylanase were stored in test tubes at 4 C. Phase separation (upper aqueous phase; lower particulate phase) was measured at 2, 24, 36 and 48 hours from homogenization (Table 2). Physical stability

(17) TABLE-US-00002 TABLE 2 Physical stability, 1 h enzymatic treatment with xylanase at 40 C. Xylanase conc. Physical stability index I.sub.phs* FXU/100 g OBF 2 h 24 h 36 h 48 h 0 67 47 40 33 100 92 82 63 55 1000 97 82 83 75 2000 98 92 83 78 *100% = no phase separation; 0% = complete phase separation

(18) About 50% of the increase in physical stability is achieved after a reaction time of merely 5 min (Table 3).

(19) TABLE-US-00003 TABLE 3 Increase in physical stability (physical stability index I.sub.phs) in respect of length of enzymatic treatment at 40 C., xylanase conc. 1000 FXU/100 g OBF Reaction time, min Storage time, h 0 5 10 15 20 25 30 2 67 97 98 95 95 95 98 24 47 97 97 93 95 93 93

(20) EXAMPLE 3. Effect of xylanase concentration on the content of soluble arabinoxylan. Soluble arabinoxylan content was measured after incubation at 40 C. of samples at different xylanase concentrations. The results are shown in Table 4 expressed as xylose equivalents.

(21) TABLE-US-00004 TABLE 4 Xylose equivalents (XE) in samples treated with different concentrations of xylanase (w/v) for 60 min Xylanase (FXU/100 g OBF) XE (mM) 0 0.38 100 7.4 1000 15.0 2000 14.0

(22) EXAMPLE 4. Particle size measurement. To establish whether the enzyme degrades cell walls and thus reduces particle size, the size of liquid oat bran base particles of the invention produced at different xylanase concentrations was measured. Control samples were not incubated with xylanase. A significant decrease in particle size was observed upon treatment with xylanase (1 h at 40 C.). Table 5 shows the mean particle diameter determined from the particle volume weight of xylanase treated samples.

(23) TABLE-US-00005 TABLE 5 Volume weight diameter of oat bran drink samples after xylanase treatment Xylanase (FXU/100 g) Mean diameter (m) Decrease (%) 0 307 100 207 32.6 1000 184 40.0 2000 154 49.8

(24) EXAMPLE 5. Effect of reaction time on soluble arabinoxylan content. Soluble arabinoxylan content was measured after the incubation of the samples for different time periods. This assay was performed to assess changes in the concentration of arabinoxylan degradation products during the reaction. Table 6 shows that there was a significant increase in arabinoxylan concentration after a reaction time of 5 min. A further, slight increase was observed at longer reaction times.

(25) TABLE-US-00006 TABLE 6 Content of soluble arabinoxylan in samples treated with xylanase (1000 FXU/100 g OBF) for different reaction times Reaction time, min 0 5 10 15 20 25 30 35 40 50 Xylose 0.5 7.7 8.2 9.6 8.3 9.1 8.9 11.1 10.7 11.4 equivalents, mM

(26) EXAMPLE 6. Effect of reaction temperature. An incubation time of 15 min was chosen since had been shown above to provide good physical stability and a substantial increase of soluble arabinoxylan. The effect of temperature variation on enzymatic degradation by xylanase was analyzed to find an optimum reaction temperature.

(27) Oat bran based drink was incubated with xylanase 1000 FXU/100 g OBF for 15 min at 40 C., 50 C., and 60 C. (Table 7).

(28) TABLE-US-00007 TABLE 7 Physical stability at 4 C. of xylanase treated oat bran based drink Xylanase, 15 min Physical stability index I.sub.phs, 4 C., % at C. 2 h 24 h 72 h No xylanase 58 42 37 40 100 97 88 50 100 93 82 60 100 97 97

(29) EXAMPLE 7. Homogenization. The physical storage stability of the liquid oat base of the invention can be further improved by homogenization. Performing homogenization in a two-step homogenizer providing a pressure of at least 150/30 bar the product shows improved physical stability even in the presence of insoluble fibers, that is, prior to decantation by which insoluble fibers are removed. Improved stability of the liquid oat base of the invention produced from whole oat (FIG. 1) and from oat bran (FIG. 2) over that of a commercial oat base (oat drink) is demonstrated in the Figures.

(30) EXAMPLE 8. Content of soluble arabinoxylan in oat bran based drink treated with xylanase at various temperatures. The known oat bran base (oat drink) described above was incubated for 15 min with 1000 FXU/100 g OBF of xylanase at 40 C., 50 C., and 60 C. The content of soluble arabinoxylan was found to have been increased at all temperatures by a factor of 5 or more (Table 8).

(31) TABLE-US-00008 TABLE 8 Soluble arabinoxylan content of xylanase treated oat bran based drink Xylanase for 15 min; C. none 40 50 60 Xylose equivalents, mM 0.89 6.6 8.7 8.1

(32) EXAMPLE 9. Particle size distribution. FIG. 3 shows the distribution of particle size of homogenized and non-homogenized oat bran base of the invention. In Table 10 corresponding volume weight diameter data are given for the following samples:

(33) For evaluating the effect of homogenization five samples were prepared: Control: Non-homogenized oat bran base not treated with xylanase; Sample A: Non-homogenized; 1000 FXU xylanase per 100 g OBF; xylanase 15 min at 60 C.; Sample B: Homogenized for 2 min; 1000 FXU xylanase per 100 g OBF; xylanase 15 min at 60 C.; Sample C: Non-homogenized, 500 FXU xylanase per 100 g OBF; xylanase 30 min at 60 C.; Sample D: Homogenized for 2 min, 500 FXU xylanase per 100 g OBF; xylanase 30 min at 60 C.

(34) TABLE-US-00009 TABLE 9 Diameter of samples A through D and of control determined from their volume weight Sample Diameter, m Decrease (%) Control 272 0 A 207 24.0 B 159 41.7 C 216 20.5 D 173 36.4

(35) As evident from Table 9 particle size reduction is more pronounced at the higher enzyme concentration.

(36) EXAMPLE 10. Preparation of oat bran drink. A beta-glucan rich (15% w/w) oat bran drink according to the invention was prepared by suspending from 7% by weight to 15% by weight of oat bran flour/enzyme mix in water. The suspension was incubated at 55 C. to 65 C. under agitation for from about 30 min to about 2 h. Incubation was stopped by heating, in particular to at least 80 C. or even 100 C. or more. The suspension was UHT treated, homogenized at a pressure of 150/30 bar, and cooled to 4 C. After storage for 20 days at 4 C. the preparation showed no significant (5% or more) phase separation. No additives had been added to the so prepared oat bran drink of the invention to stabilize it against phase separation. Alternatively the oat bran drink of the invention prepared in this manner can be pasteurized.

(37) EXAMPLE 11. Dried oat bran drink. Oat bran drink of Example 11 was dried to a white powder by spray drying using equipment for spray drying cow milk. The powder can be used for reconstitution of the drink by suspending it in water or as a food additive.

(38) EXAMPLE 12. Preparation of a whole grain oat drink. The procedure followed was essentially that of Example 10 except for that whole grain oat flour was used as starting material.

(39) EXAMPLE 13. Dried whole oat grain drink. Whole grain oat drink of Example 12 was dried to a white powder by spray drying using equipment for spray drying cow milk. The powder can be used for reconstitution of the drink by suspending it in water or as food additive.

(40) EXAMPLE 14. Preparation of a fruit flavored drink comprising oat bran drink. Several samples were prepared by mixing from 25% (w/w) to 95% (w/w) of oat bran drink of Example 10 or reconstituted drink according to Example 11 with fruit concentrate of desired flavor. The mixtures were cooled to 4 C. and bottled under aseptic conditions. The drinks proved to be stable for three weeks at this temperature in absence of any stabilizing food additives.

(41) EXAMPLE 15. Preparation of a fruit flavored drink comprising whole grain oat drink. Several samples were prepared by mixing from 25% (w/w) to 95% (w/w) of whole grain oat drink of Example 12 or reconstituted drink according to Example 13 with fruit concentrate of desired flavor. The mixtures were cooled to 4 C. and bottled under aseptic conditions. The drinks proved to be stable for three weeks at this temperature in absence of any stabilizing food additives.

(42) EXAMPLE 16. Preparation of a nutritious high fiber drinking yogurt based on fermented oat bran drink and cow milk. From 50% by weight to 95% or more by weight (several samples prepared) of the oat bran drink of Example 10 or such drink reconstituted according to Example 11 were mixed with standard cow milk. The mixture was passed through a heat exchanger. The mixture was pasteurized and subsequently cooled to about 40 C. to about 50 C. followed by inoculation with the required quantity of desired bacterial culture. The culture may optionally comprise probiotic strains. The blend was thoroughly mixed and fermented until it reached a pH of about 4.5. The fermented product can be flavored with spices to provide a savory type of drinking yoghurt or a fruit flavored drinking yoghurt by adding a fruit concentrate of desired flavor under aseptic conditions. The drinking yoghurt is then bottled under aseptic conditions and stored at +4 C. The drinking yoghurt proved to be stable for three weeks at this temperature in absence of any stabilizing food additives.