Food or edible material: processes – compositions – and products – Products per se – or processes of preparing or treating... – Gels or gelable composition
Reexamination Certificate
1998-11-05
2001-04-24
Hendricks, Keith (Department: 1761)
Food or edible material: processes, compositions, and products
Products per se, or processes of preparing or treating...
Gels or gelable composition
C426S050000, C426S583000, C426S599000, C426S580000, C536S002000
Reexamination Certificate
active
06221419
ABSTRACT:
The present invention relates to a pectin for stabilising proteins particularly for use in stabilising proteins present in aqueous acidic beverages. The invention further provides stabilised acidic beverages as well as a process for preparing the pectin.
BACKGROUND OF THE INVENTION
Acidified milk drinks are becoming increasingly popular amongst consumers. Such drinks have long been commercially successful in Japan and parts of south east Asia and are now being introduced into western markets. Such drinks may be yoghurt-based (in which case they are often called drinking yoghurts), Lactobacillus drinks or soft drinks based upon milks These drinks differ from each other for instance in their respective contents of milk solids non-fat (MSNF). MSNF is principally casein. Yoghurt drinks typically contain a minimum of 8% by weight of MSNF, Lactobacillus drinks contain a minimum of 3% by weight of MSNF, whereas soft drinks contain less than 3% by weight of MSNF.
Drinking yoghurts are either distributed fresh and promoted for their content of live lactobacilli, or heat treated prior to distribution to obtain extended shelf life. Heat treated yoghurt drinks must be stabilised to prevent sedimentation of casein particles as such sedimentation leads to the drinks developing an undesirable sandy mouth feel. Even low viscosity MSNF fresh acidified milk drinks have to be stabilised to prevent precipitation of casein particles.
Pectin is most commonly used as the stabiliser for acidified milk drinks. Pectin is a structural polysaccharide commonly found in the form of protopectin in plant cells. The backbone of pectin comprises &agr;-1-4 linked galacturonic acid residues which are interrupted with a small number of 1,2 linked &agr;-L-rhamnose units. In addition, pectin comprises highly branched regions with an almost alternating rhamno-galacturonan chain. These highly branched regions also contain other sugar units attached by glycosidic linkages to the rhamnose or galacturonic acid units. The long chains of &agr;-1-4 linked galacturonic acid residues are commonly referred to as “smooth” regions, whereas the highly branched regions are commonly referred to as “hairy” regions.
Some of the carboxyl groups of the galacturonic residues are esterified, typically by methyl groups. The remainder are present as free carboxyl groups. Esterification of the carboxyl groups occurs after polymerisation of the galacturonic acid residues. However, it is extremely rare for all of the carboxyl groups to be esterified. Usually, the degree of esterification varies from 0 to 90% of the available carboxylic groups. If 50% or more of the carboxyl groups of a pectin are esterified, then the pectin is commonly referred to as being a high ester pectin or high methoxyl pectin. If less than 50% of the carboxyl groups are esterified, then the pectin is commonly referred to as being a low ester pectin or a low methoxyl pectin. If the pectin does not contain any, or only a few, esterified groups, it is commonly referred to as pectic acid.
The structure of the pectin, in particular the degree of esterification, dictates many of its physical and/or chemical properties. For example, pectin gelation caused by the presence of calcium cations depends especially on the degree of esterification. Gelation is believed to result from the calcium ions forming cross-linked complexes with free carboxyl groups of a number of pectin chains causing the formation of a continuous three-dimensional gelled matrix.
It is known that the distribution of the free carboxyl groups along the polymer chain is important for determining whether the pectin is suitable for use as a stabiliser for acidified milk drinks. It has been proposed that pectin stabilises a suspension of casein particles by adsorbing onto the surface of the casein particles at specific points of the pectin molecule. The remainder of the pectin molecule forms dangling chains and loops that protrude into the liquid phase. The repulsion between the resulting complexed particles may be due to the increased osmotic pressure created when pectin chains complexed to two casein particles interact with one another.
For a pectin to be useful as a stabiliser of an acidified milk drink at least some of its free carboxyl groups have to be arranged in blocks (i.e. contiguously) rather than being randomly distributed discretely along the polymer chain. The binding force between a pectin molecule and a casein particle is due to the blocks of negatively charged carboxyl groups interacting with positive charges which exist on the particle surface. The length of the blocks of free carboxyl groups is also important. Blocks of carboxyl groups that are either too long or too short do not result in stabilization of the system. In the former case, no dangling chains exist. In the latter case, the pectins do not securely attach themselves to the casein particles and therefore do not lead to stabilisation of the particles.
A well-known characteristic of low ester or calcium sensitive pectin is its ability to thicken or form gels, particularly when in the presence of alkaline earth metal cations such as Ca++. Unfortunately, acidified milk drinks naturally contain significant quantities of calcium cations. These cations have the undesirable effect of causing significant viscosity increases if excess pectin is present which can even result, in extreme cases, in the acidified milk drink gelling.
Production of heat-treated whey drinks also presents problems. Heat treatments above 70° C. cause variable amounts of whey particles to form depending upon the precise temperature reached. The amount of pectin necessary to stabilise the heat-treated whey drink therefore varies with the heat treatment. As the whey particles that are formed are relatively small, the amount of pectin needed to obtain a stable drink can be very high due to the large total surface area of these particles. However, excessive addition of pectin will again result in thickening or gel formation due to cross-linking of the excess pectin with the naturally present calcium cations.
It will therefore be understood that the inclusion of pectin has both desirable and undesirable effects on the properties of acidified milk drinks. Whilst it can act as a stabiliser against sedimentation of casein particles or whey separation, it can have the disadvantage of increasing the viscosity of the drink due to its cross-linking with naturally co-present calcium cations rendering the drink unpalatable. It will be seen that in the absence of pectin, there is significant sedimentation in the case of both drinks caused by the instability of the casein particles which also results in relatively high viscosity. After a certain concentration of pectin has been added, the casein particles become stabilised against sedimentation after which increasing the pectin concentration has little effect on sedimentation. Turning to the viscosity of the drinks, this also significantly drops on stabilisation of the casein particles but then almost immediately begins to rise again due to cross-linking of the excess pectin added by the co-present calcium cations. This increased viscosity is undesirable as it leads to the beverage having poor organoleptic properties. This range may be as narrow as only 0.06% by weight of pectin based upon the beverage weight as a whole. Below this working range, sedimentation is a significant problem, whereas above it, the viscosity of the beverage is undesirably high.
Commercially, it is critical for manufacturers of acidified milk drinks to avoid sedimentation as this would ruin the drink. Therefore manufacturers typically add excess pectin to ensure that sedimentation does not occur but the excess pectin which is added results in the drinks having an undesirably high viscosity. Whilst manufacturers of course would like to target the narrow working range previously mentioned, this is commercially difficult due to the risk that insufficient pectin may be added causing the whole batch of drink to fail due to sedimentation.
It is well known t
Greenblum & Bernstein P.L.C.
Hendricks Keith
Hercules Incorporated
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