Food or edible material: processes – compositions – and products – Products per se – or processes of preparing or treating... – Basic ingredient lacteal derived other than butter...
Reexamination Certificate
2001-02-01
2003-12-16
Wong, Leslie (Department: 1761)
Food or edible material: processes, compositions, and products
Products per se, or processes of preparing or treating...
Basic ingredient lacteal derived other than butter...
C426S522000, C426S573000
Reexamination Certificate
active
06663911
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of making sterilized milk compositions comprising native gellan gum, wherein the native gellan gum has been pre-treated with a denaturing agent. The present invention further relates to the resulting sterilized milk compositions and to the milk-based gellan food products.
2. Related Background Art
Gellan gum is an extracellular polysaccharide produced by the bacteria
Sphingomonas elodea
. A number of
S. elodea
strains produce gellan gum with differing characteristics, including S-60, LPG-2, PDG-1 and PDG-4. Gellan gum produced by
S. elodea
is commercially available as Kelcogel LT100® from CP Kelco in San Diego, Calif.
Commercially, gellan gum is formed by inoculating a fermentation medium under aerobic conditions with
S. elodea
bacteria. The fermentation medium contains a carbon source, phosphate, organic and inorganic nitrogen sources and appropriate trace elements. The fermentation is conducted under sterile conditions with strict control of aeration, agitation, temperature and pH. Upon completion of the fermentation, the viscous broth is pasteurized to kill viable cells prior to recovery of the gum.
The primary structure of gellan gum comprises the sugars glucose, glucuronic acid and rhamnose in a 2:1:1 molar ratio, which are linked together, as depicted below, to form a tetrasaccharide repeat unit. In the native form, gellan gum is modified by acetyl and glyceryl substituents on the same glucose residue. On average, there is one glycerate substituent per tetrasaccharide repeat unit and one acetate substituent per every two tetrasaccharide repeat units. The chemical structure of native gellan gum may be depicted as follows:
wherein n is between about 500 and about 2500. Gellan gum displays different characteristics depending upon the method of recovery from the fermentation broth. Direct recovery from the fermentation broth yields gellan gum in its native, high acyl form, which is modified by
S. elodea
with acetyl and glyceryl substituents on one glucose residue. Isolation of gellan gum in this native, high acyl form yields a soft, flexible gel. At low dosage levels, gellan gum is characterized by very high low-shear viscosity and true yield stress.
The texture of native gellan gum is ideal for a number of commercial food applications, including milk-based products such as puddings, coffee creamers, drinks and desserts. The rheology of gellan gum at low dosage enables it to suspend fine particles such as cocoa in milk systems. As a result of these textural characteristics, gellan gum has long been sought for use in cultured dairy products, retorted dairy products and frozen dairy products.
Unfortunately, however, an off-flavor and odor develop in the shelf-stable, milk-based gellan products after a short time that renders the food product unpalatable. The off-flavor and odor have been described as reminiscent of a cleaning chemical or of fecal matter. Analysis of the food product has linked the off-flavor and odor to the development of a chemical called para-cresol, which is detectable in milk-based gellan products that have been treated at ultra high temperatures and further stored at room temperature. The development of para-cresol in sterilized milk compositions comprising native gellan gum limits their potential commercial applications for products that require long-term storage, including many beverages and puddings.
Several attempts have been made to modify gellan gum to render it usable in dairy products sterilized by ultra-high temperature treatment. Deacylation of the glucose moiety, while effective at eliminating para-cresol, nonetheless changes the texture of the gellan gum, making it more brittle and less conducive for use in food applications.
It would be advantageous to provide a method of making a sterilized milk composition comprising native gellan gum that eliminates or reduces para-cresol development without undue change to the composition's taste, odor or textural characteristics.
SUMMARY OF INVENTION
The present invention provides a method of making sterilized milk compositions comprising native gellan gum, wherein the native gellan gum has been pre-treated with a denaturing agent. The method comprises the step of pre-treating native gellan gum with a denaturing agent such as a common oxidative agent or an alkaline caustic agent prior to mixing and sterilizing the native gellan/milk composition. Preferably, treatment of the native gellan gum with the denaturing agent results in reduction of para-cresol levels in the sterilized native gellan/milk composition to below 25 parts per billion (ppb) after 12 months of storage, and most preferably, to levels where para-cresol is undetectable by taste.
In one preferred embodiment of the present invention, the denaturing agent of the present invention is a common oxidative agent such as sodium hypochlorite. In an alternative embodiment, the denaturing agent is a caustic agent such as potassium hydroxide. In a preferred embodiment of the invention, the native gellan gum is further pre-treated by enzymes such as lysozyme and/or protease.
The present invention is further directed to the food products comprising the treated gellan gum and the sterilized milk.
DETAILED DESCRIPTION OF THE INVENTION
As defined herein, sterilization refers to treatment at ultra-high temperatures of over 138° C. for over 2 seconds. Most preferably, sterilization is performed at about 140-150° C. for approximately 4-6 seconds. After sterilization and packaging in air-tight containers, sterilized milk may be stored at room temperature for up to 12 months without degradation.
It is known that para-cresol develops in sterilized milk when the enzymes glucuronidase and aryl sulfatase have been added (J. Agr. Food Chem. Vol. 1, 1973). It is believed that when native gellan gum is combined with milk and sterilized, small amounts of the residual enzymes found in native gellan gum(presumably glucuronidase and aryl sulfatase) survive the ultra-high temperature heat processing. Over time, these residual enzymes in the native gellan gum cleave the naturally occurring para-cresol conjugates in the sterilized native gellan/milk composition to generate free para-cresol.
Without being bound by theory, it is furthermore believed that para-cresol production can be disrupted by denaturing the residual enzymes that reside in the native gellan gum. In particular, para-cresol production can be interrupted by addition of a denaturing agent.
The denaturing agent of this invention is any agent capable of disrupting the enzymatic pathway by which para-cresol is produced. In one preferred embodiment, the denaturing agent is an oxidative agent, such as hydrogen peroxide, ozone or any of the hypochlorite salts. Most preferably, the oxidative agent is sodium hypochlorite.
In another preferred embodiment, the denaturing agent is an alkaline caustic agent selected from the group consisting of hydroxide salts, carbonate salts, alkaline phosphate salts or other alkaline caustic agents well-known in the art. Preferred alkaline caustic agents include potassium hydroxide (KOH), sodium hydroxide (NaOH), trisodium- or tetrasodium-polyphosphate.
Additional steps may be performed to optimize para-cresol reduction. A further optional step of adding a chelating agent may be performed during treatment with the denaturing agent. In addition, after treatment with the denaturing agent and the optional chelating agent, the native gellan gum may be subjected to treatment with lysozyme or protease to break up residual cellular debris. Alternatively, if a caustic agent such as KOH is used, then lysozyme may be added prior to addition of KOH, so that the lysozyme may function at its optimal pH, which is acidic to neutral. In this alternative method, the gellan gum is treated first with lysozyme, followed by treatment with the alkaline caustic agent and optional neutralization, then treatment with a protease. The protease is capable of reacting at a pH of about 8 or higher. This lat
Morrison Neil A.
Valli Raymond C.
Banner & Witcoff , Ltd.
C. P. Kelco U.S., Inc.
Wong Leslie
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