Method of preparing lactose-hydrolyzed milk with suppressed sweetness

A lactose-hydrolyzed fluid milk comprising fluid milk, the normal lactose content of which has been reduced by at least about 70% by lactase hydrolysis, having incorporated therein from about 0.01 to about 0.15% by weight of potassium chloride, a process for its preparation and a method of suppressing perceived sweetness of lactose-hydrolyzed milk by incorporating therein potassium chloride.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
This invention relates to fluid milk in which a major amount of the lactose 
present therein has been hydrolyzed by lactase enzymes and to milk 
products derived therefrom and more specifically to such fluid milk and 
milk products which incorporate potassium chloride to counteract increased 
sweetness resulting from lactose hydrolysis. 
(b) Information Disclosure Statement 
It is generally known that milk and milk products contain high percentages 
of lactose. For example, the lactose content of regular homogenized 
pasteurized milk (3.5% butterfat) is 4.9%, of lowfat milk (2% butterfat) 
is 6.0%, and of fluid skim milk is 5.1%. 
It is well known to those familiar with the state-of-the-art, that there 
exists a significant population which cannot totally digest lactose. This 
population is generally referred to in the professional literature as 
lactose intolerant. The estimated number of individuals exhibiting lactose 
malabsorption in the USA is between 28 and 75 million. The incidence in 
certain population sub-groups is significantly higher than others. For 
example, it is estimated that lactose intolerance in American blacks may 
be over 60%, whereas the incidence in American whites is less than 25%. 
It is generally believed that individuals suffering from lactose 
intolerance have lactase deficiency. Several approaches have been 
undertaken by the industry to alleviate this problem. Generally, these 
approaches may be classified into two categories: 
(1) Providing to the lactose intolerant individual an enzyme preparation 
which contains a stabilized form of lactase. This preparation is ingested 
within a prescribed time prior to or with the ingestion of the lactose 
containing products. 
(2) Hydrolyzing the lactose using lactase enzymes prior to its ingestion. 
For example, lactase enzymes are added to fluid milk and sufficient time 
is allowed to assure the hydrolysis of the lactose into glucose and 
galactose. 
Lactase is a trivial name for the .beta.-galactosidases which catalyze the 
hydrolysis of lactose to its component saccharides, glucose and galactose. 
Sources of lactase, including commercial sources, are described in the 
literature. See, for example, R. R. Mahoney, Developments In Dairy 
Chemistry, Chapter 3, Edited by P. F. Fox, Elsevier Applied Science 
Publishers, 1985. Lactase enzymes used in processing dairy foods are 
derived from the yeasts Kluyveromyces fragilis, Kluyveromyces lactis and 
Clandida pseudotropicalis. Lactase enzymes are available both in liquid 
form, e.g., as solutions in water/glycerin, or in powder form. The 
activity of these enzymes is based on neutral lactase units (NLU) as 
determined by assay and falls in the range of from approximately 1000 to 
5000 NLU/gram. It requires one gallon of 1000 NLU/gram activity product to 
convert 1000 gallons of milk to a 70% lactose hydrolysis level in 
twenty-four hours when the milk is stored at 40.degree. F. Conversely, it 
requires 1/5 of a gallon of 5000 NLU/gram activity product to accomplish 
70% lactose hydrolysis in twenty-four hours when the milk is stored at 
40.degree. F. 
The Food and Drug Administration has determined that hydrolyzed lactose 
products must contain at least 70% less lactose than the non-hydrolyzed 
product. Lactose-hydrolyzed, ultra-pasteurized or pasteurized milk 
containing at least 70% less lactose have been available in the USA for 
several years. 
The literature describes several methods for hydrolyzing the lactose (see 
R. R. Mahoney, supra). The most widely used process today involves the 
addition of lactase enzymes and incubation at 40.degree. F. for the 
necessary time to achieve at least 70% lactose hydrolysis. The major 
disadvantage of this method is the cost of the enzyme. Another problem 
associated with this process is the inability to control closely the end 
point of the hydrolysis. This is because of the time required to 
inactivate the enzyme in a whole batch of milk in a commercial dairy. To 
overcome these problems a continuous process using immobilized enzymes was 
proposed. However, this process is not commercially utilized for the 
hydrolysis of milk at this time. 
Since glucose and galactose, the products of hydrolyzed lactose, are 
sweeter than lactose, lactose-hydrolyzed milk, when tasted, is sweeter 
than regular milk. This detracts significantly from its consumer 
acceptance. 
Jacober-Pivarnik et al., Journal of Food Science, 49, 435-438, 445 (1984), 
disclose an enzyme assay that can be used to accurately reflect lactase 
activity using a nonfat dry milk substrate. The assay was used to evaluate 
the effect of potassium ions, incorporated as potassium chloride, as a 
stabilizer and activator on four yeast lactase enzymes. In the description 
of the procedure used in studying the effect of potassium ion, it is 
disclosed that a concentration of 36 mM KCl, i.e., about 0.27% by weight, 
was used throughout the study since it reflected the level of potassium 
ions present in milk. 
SUMMARY OF THE INVENTION 
Since the excess sweetness of lactose-hydrolyzed milk detracts from 
consumer acceptance, it is evident that a need exists for a more 
acceptable lactose-hydrolyzed milk. It has now unexpectedly been found 
that the addition to lactose-hydrolyzed milk of potassium chloride within 
a critical range of concentrations suppresses the perceived sweetness of 
the milk resulting from glucose and galactose formed by hydrolysis of the 
lactose, thus increasing its consumer acceptance. 
Thus, in one aspect, the invention provides a lactose-hydrolyzed fluid milk 
comprising fluid milk, the normal lactose content of which has been 
reduced by at least about 70% by lactase hydrolysis, having incorporated 
therein from about 0.01 to about 0.15% by weight of potassium chloride. 
In another aspect, the invention provides a method of suppressing perceived 
excess sweetness of lactose-hydrolyzed fluid milk the normal lactose 
content of which has been reduced by at least about 70% by lactase 
hydrolysis which comprises incorporating in the milk from about 0.01 to 
about 0.15% by weight of potassium chloride.

DETAILED DESCRIPTION INCLUSIVE OF PREFERRED EMBODIMENTS 
As used herein the term "normal lactose content" refers to the amount of 
lactose inherently present in milk as obtained from the cow; and the term 
"lactose-hydrolyzed milk" refers to dairy milk the normal lactose content 
of which has been reduced to at least about 70% by the hydrolysis of the 
lactose by lactase enzyme and includes whole milk, lowfat milk (e.g., 1-2% 
butterfat content) and nonfat milk. 
Dairy milk as obtained from the cow inherently contains both potassium and 
chloride ions. Therefore, it will be understood that in practicing the 
invention, the potassium chloride incorporated in the dairy milk in 
accordance with this invention is from an external source, i.e., is in 
addition to the potassium and chloride ions inherent in the dairy milk. 
The potassium chloride incorporated in the lactose-hydrolyzed milk should 
be of food or USP grade. The concentration to be incorporated is in the 
range of from about 0.01 to about 0.15 percent by weight. Preferably the 
percent by weight concentration is in the range of from about 0.02 to 
about 0.075, and more preferably from .about 0.03 to about 0.06, 
especially from about 0.04 to about 0.05 and optimally about 0.04. 
The potassium chloride can be added to the milk at any stage in its 
processing for consumption. Thus it can be added prior to or during the 
incubation of the milk with lactase or subsequent thereto. In the latter 
case, it can be added at the dairy where the milk is processed or after 
purchase by the consumer. When added by the consumer it can be in any 
convenient form, e.g., in liquid or tablet form. For example, there 
currently is commercially available to the consumer lactase preparations 
in liquid form for addition to milk which has not been subjected to 
lactase treatment in order to reduce its lactose content. Such preparation 
could additionally have incorporated therein potassium chloride in an 
amount which will provide the concentration required in the milk in 
accordance with the invention. 
The potassium chloride, when added to the milk during processing, can be 
incorporated by any standard procedure. For example, it can conveniently 
be incorporated by sprinkling the appropriate amount into the milk and 
gently agitating the milk until the potassium chloride is dissolved. 
The invention is illustrated by the following examples without, however, 
being limited thereto. 
A test was conducted to evaluate the relative sweetness of two commercially 
available skim milks, one regular, i.e., not lactose-hydrolyzed, and the 
other lactose-hydrolyzed. The degree of lactose hydrolysis was determined 
using a cryoscope and confirmed by HPLC and found to be 80%. The two skim 
milks were evaluated using an expert panel consisting of individuals 
selected for their taste acuity and trained in flavor profiling 
techniques. In this test the expert panel consisted of seven individuals 
and the test was carried out two times for a total of fourteen 
observations. 
All samples submitted to the expert panel were coded. The skim milks were 
evaluated for the following attributes: 
______________________________________ 
Sweet on a scale of 0 (none) to 8 (very sweet) 
Bitter on a scale of 0 (none) to 8 (very bitter) 
Salt on a scale of 0 (none) to 8 (very salty) 
Sour on a scale of 0 (none) to 8 (very sour) 
Overall quality 
on a scale of 0 (dislike extremely) to 
8 (like extremely) 
______________________________________ 
The results of the expert panel's evaluation, expressed as a mean of the 
scores, are summarized below where A represents the regular skim milk and 
B represents the lactose-hydrolyzed skim milk. 
______________________________________ 
Attribute A B 
______________________________________ 
Sweet 1.0 3.5* 
Sour 0.5 1.0 
Salty 0 0 
Bitter 0 0.1 
Overall quality 6.4 3.0* 
______________________________________ 
*Significantly different from control at the 99% confidence level 
These results clearly show that the lactose-hydrolyzed skim milk (B) is 
sweeter and less acceptable than the regular skim milk (A). 
EXAMPLE 1 
Potassium chloride was added to samples of the same lactose-hydrolyzed skim 
milk used in the above described test. The levels of potassium chloride 
incorporated in the milk were 0.05, 0.075, 0.1, 0.15 and 0.5 wt-%. These 
samples and samples of the lactose-hydrolyzed skim milk to which no 
potassium chloride had been added (control samples) were evaluated for 
their attributes on a scale of 0 to 8 by the same expert panel of seven 
individuals used in the test described above. All samples submitted to the 
expert panel were coded. The results, expressed as a mean of the scores, 
are summarized below. 
______________________________________ 
Lactose-Hydrolyzed Skim Milk 
KCl level: 
Control 
0.05 0.075 0.10 0.15 0.5 
______________________________________ 
Sweet 3.5 2.5* 2.0* 2.0* 2.2* 2.0 
Sour 1.0 1.2 1.2 0.8 1.3 1.2 
Salty 0 0.3 0.3 0.3 0.5 0.3 
Bitter 0.1 0 0.5 0.1 0.5 0.8 
Overall Quality 
3.0 4.0* 4.3* 4.5* 3.7** 3.2 
______________________________________ 
*Significantly different from control at the 99% confidence level 
**Significantly different from control at the 99% confidence level 
These results clearly show that the incorporation of potassium chloride in 
lactose-hydrolyzed skim milk of between 0.05 and 0.5 weight-percent 
reduces the perceived sweetness of the milk. Furthermore, improvement in 
the overall quality of the milk was noted in the range of 0.05 to 0.15 
weight-percent of potassium chloride. 
EXAMPLE 2 
Lowfat milk (1% butterfat) was processed at a UHT (ultrahigh temperature) 
plant facility as follows: 
To pasteurized lowfat milk, lactase enzyme having an activity of 955 NLU/g 
was added to provide a concentration of 0.02% enzyme. The lowfat milk 
containing the enzyme then was incubated in a refrigerator at 40.degree. 
F. The temperature of the milk was measured at 42.degree. F..+-.2.degree. 
F. The degree of hydrolysis was determined using a cryoscope. To 70% 
lactose-hydrolyzed milk so prepared was added sufficient potassium 
chloride to provide 0.075 weight-percent concentration. The milk then was 
subjected to UHT treatment and aseptically packaged in gallon containers. 
Two controls also were prepared, one a non-hydrolyzed lowfat milk, i.e., 
lowfat milk (1% butterfat) which was not lactose-hydrolyzed, and the other 
70% lactose-hydrolyzed lowfat milk (1% butterfat), both UHT treated and 
neither containing potassium chloride. The three milk products were 
evaluated by the same taste panel of seven individuals with the following 
results (expressed as a mean of the scores). 
______________________________________ 
Control Control 70% lactose- 
(no lactose 
(70% lactose 
hydrolyzed lowfat 
hydrolysis) 
hydrolysis) 
milk + 0.075 wt % 
Attribute (no KCl) (no KCl) KCl 
______________________________________ 
Sweet 1.5 3.0 2.2* 
Sour 0.5 0 0 
Salty 0 0 0 
Bitter 0 0 0 
Overall Quality 
6.2 4.0 4.8* 
______________________________________ 
*Significantly different from lactosehydrolyzed control at 95% confidence 
level 
These results clearly show that the addition of potassium chloride to 
lactose-hydrolyzed lowfat milk reduces the perceived sweetness and 
increases the overall quality thereof. 
EXAMPLE 3 
Lactose-hydrolyzed nonfat and lowfat (1% butterfat) milk containing 0.04 
wt-% (1.5 g/gal) of potassium chloride each were prepared by a procedure 
similar to that described in Example 2 and their attributes where compared 
with the corresponding lactose-hydrolyzed nonfat and lowfat milk to which 
in each case no potassium chloride had been added. These milk samples were 
evaluated for their attributes by an expert panel of ten individuals on a 
scale of 0 to 8 as described above. The results, expressed as a mean of 10 
scores, are summarized below. 
______________________________________ 
Lactose-Hydrolyzed Milk 
Nonfat Lowfat 
Attribute 
With KCl No KCl With KCl 
No KCl 
______________________________________ 
Sweet 1.4 2.4* 0.4 0.9** 
Sour 0.3 0.3 0 0 
Salty 0.1 0 0 0 
Bitter 0.2 0.2 0.2 0 
Off-flavor.sup.a 
0 0.1 0 0 
______________________________________ 
.sup.a 0 = none, 8 = very strong 
*Denotes significance at the 99% confidence level using paired ttest 
**Denotes significance at the 95% confidence level using paired ttest 
These results clearly show that the sweetness of the lactose-hydrolyzed 
milk was reduced by the addition of 0.04 wt-% of potassium chloride. 
EXAMPLE 4 
Lactose-hydrolyzed lowfat (1% and 2% butterfat) and nonfat milk each 
containing concentrations of KCl of 0, 0.02, 0.03, 0.04, 0.05 and 0.075 
were prepared by procedures similar to that described in Example 2 and 
evaluated by an expert panel of 10 individuals for their attributes on a 
scale of 0 to 8 in order to determine the optimum concentration of 
potassium chloride. All samples were coded. The results, expressed as a 
mean of 10 scores, are summarized below. 
______________________________________ 
EFFECT OF THE ADDITION OF 
POTASSIUM CHLORIDE 
TO LACTOSE HYDROLYZED 
MILK 
Sweetness Level of 
KCl Concentration wt % 
Intensity Rating 
Aftertaste 
______________________________________ 
Lowfat Milk (2%) 
0.0 2.0 0.2 
0.02 2.2 0.2 
0.03 1.5 0.2 
0.04 0.9 0.2 
0.05 1.0 0.4 
0.075 1.2 0.7 
Lowfat Milk (1%) 
0.0 2.4 0.0 
0.02 1.7 0.1 
0.03 1.5 0.2 
0.04 0.7 0.3 
0.05 0.8 0.3 
0.075 1.2 0.6 
Nonfat Milk 
0.0 2.1 0.2 
0.02 1.9 0.3 
0.03 1.6 0.3 
0.04 0.7 0.3 
0.05 0.9 0.3 
0.075 1.3 1.0 
______________________________________ 
These results clearly indicate that the addition of potassium chloride 
reduces the perceived sweetness of the lactose-hydrolyzed milk, the 
optimum concentration of KCl being about 0.04 wt-%. 
EXAMPLE 5 
Two ultra-pasteurized lactose-hydrolyzed lowfat (1% butterfat) milks, one 
having incorporated therein 0.04 wt-% potassium chloride and prepared by a 
procedure similar to that described in Example 2, and the other obtained 
from a commercial source and having no potassium chloride incorporated 
therein were compared to a control. The control was a pasteurized lowfat 
(1% butterfat) milk, obtained from a commercial source, which neither had 
been lactose-hydrolyzed nor had potassium chloride incorporated therein. 
The purpose of the comparative test was to determine which of the two 
lactose-hydrolyzed milks was closest, or most similar, in taste to the 
control. An expert panel of ten individuals participated in the test. All 
samples of milk were coded. The panelists were instructed to taste the 
control sample first and then the test sample in the order presented on a 
tray, from left to right, and that after the first round of testing in 
order, they could switch back and forth between the test samples and 
retaste the control sample as often as needed to refresh their taste 
memory. A similar comparative test was conducted with two corresponding 
samples of nonfat milk and a corresponding nonfat milk control. 
In the above described comparative tests, 9 of the 10 panelists selected 
the lactose-hydrolyzed lowfat milk with incorporated potassium chloride as 
being closest in taste to the control; and all 10 of the panelists 
selected the lactose-hydrolyzed nonfat milk with incorporated potassium 
chloride as being closest in taste to the control. 
EXAMPLE 6 
Nonfat and lowfat (1% butterfat) milk were hydrolyzed at a dairy plant. 
Once the degree of hydrolysis exceeded 80%, 500 gallons of each 
lactose-hydrolyzed milk was transferred to a tank. The remainder (control) 
was passed through the UHT process and packaged. To the 500 gallon sample, 
0.04 wt-% of potassium chloride was added and thoroughly mixed to assure 
complete dissolution. This potassium chloride containing 
lactose-hydrolyzed milk was passed through the same UHT process as the 
control and packaged. Samples of the control and the treated 
lactose-hydrolyzed milks were analyzed for the degree of lactose 
hydrolysis using HPLC. The milks were subjected to an expert taste panel 
six days and six weeks after production. All samples were coded. The 
results, expressed as a mean of the scores, for the nonfat and lowfat milk 
are summarized below. 
______________________________________ 
Lactose-Hydrolyzed Nonfat Milk 
With 0.04% KCl Added 
After 
Attributes Control 6 Days* After 6 Weeks* 
______________________________________ 
Sweet 2.4 1.4** 1.0** 
Sour 0.3 0.3 0.3 
Salty 0.0 0.1 0.0 
Bitter 0.2 0.2 0.0 
Off-flavor 0.1 0.0 0.0 
% Lactose hydrolysis 
82.1 81.8 81.8 
______________________________________ 
*Stored at 40.degree. F. 
**Significantly different from control at the 95% confidence level using 
ttest statistic 
______________________________________ 
Lactose-Hydrolyzed Lowfat Milk 
With 0.04% KCl Added 
After 
Attributes Control 6 Days* After 6 Weeks* 
______________________________________ 
Sweet 1.1 0.4** 0.4** 
Sour 0.0 0.0 0.3 
Salty 0.0 0.0 0.2 
Bitter 0.2 0.2 0.0 
Off-flavor 0.0 0.0 0.2 
% Lactose hydrolysis 
84.4 83.3 83.3 
______________________________________ 
*Stored at 40.degree. F. 
**Significantly different from control at the 95% confidence level using 
ttest statistic 
The above results clearly indicate that the addition of 0.04% KCl decreased 
the perceived sweetness level significantly without increase in the 
perceived off-flavor level. The results further show that no changes in 
the product flavor were noticed after up to 6 weeks of storage. 
EXAMPLE 7 
Two ultra-pasteurized lactose-hydrolyzed lowfat (1% butterfat) milks, one 
having 0.04 wt-% potassium chloride incorporated therein and prepared by a 
procedure similar to that described in Example 2, and the other obtained 
from a commercial source and having no potassium chloride incorporated 
therein, were compared with a control. The control was a pasteurized 
lowfat (1% butterfat) milk obtained from a commercial source which neither 
had been lactose-hydrolyzed nor had potassium chloride incorporated 
therein. The purpose of the test was the same as for that described in 
Example 5. However, in this case the comparison was made by twenty 
consumers recruited from the same geographic area, all of whom were 
regular users of lowfat and nonfat milks. The consumers were each given a 
coded sample of the two lactose-hydrolyzed milks and the control and 
instructed to taste the control and the two lactose-hydrolyzed samples and 
to select which of the latter two samples was closest in taste to the 
control. A similar comparative test was conducted with the same twenty 
consumers with two corresponding samples of nonfat milk and a 
corresponding nonfat control. 
In the above described comparative tests, seventy percent of the consumers 
chose the lactose-hydrolyzed lowfat milk with incorporated potassium 
chloride as being closest in taste to the control; and eighty-five percent 
of the consumers chose the lactose-hydrolyzed nonfat milk with 
incorporated potassium chloride as being closest in taste to the control.