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Whey Research Sponsored by CDRF
Scientific
Literature Review on Protein-Based Edible Films - Mary Ann Augustin, Food
Science Australia
Scientific
Literature Review on Protein-Based Edible Films Executive summary The California Dairy Research Foundation commissioned Food Science Australia to carry out a literature search on the use of milk proteins, used alone or in combination with other proteins, lipids and other components to form edible films. This literature review focused on edible films made from milk proteins. Information on other proteins was also included in this survey, as was limited information on other edible films based on polysaccharides or lipids. The literature search results were organized into the following areas: - Overview of developments in edible films with a focus on protein-based films - Factors affecting the properties of milk protein films - Factors affecting the properties of protein films (other than milk protein-based films) - Factors affecting gloss - Controlling the properties of milk protein films - Opportunities for using edible films as antimicrobial agents - Current status of edible films The literature search demonstrated that many researchers have examined proteins as well as a range of other food-grade ingredients for the development of edible films. The benefits of edible film packaging have been espoused for many years, but it appears that the uptake of the technology on a commercial scale has been limited compared to the technical success of edible films and coatings on a laboratory scale. Many factors should be considered when commercializing a technology developed in a research environment. It is essential to understand the competitiveness of the technology in the market place and to establish the need for the technology. Ensuring that appropriate intellectual property protection is in place and that the new ingredient is cost-competitive compared to alternate film formulations are important. To take the milk protein edible film technology to the market place requires consideration of: - The consistency of the functionality of milk protein-based edible films - The science that enables solutions of technical issues that arise during adoption of the technology - Consistency of supplied milk protein ingredients - Storage stability of milk protein ingredients - The ability of the milk protein-based films to be matched to the targeted application - The usefulness of films in target applications - Anticipation of changes that may be required in the end-user’s process - The opportunity for the milk protein-based films to be used for purposes other than its barrier and mechanical properties - Improving food safety - Increasing level of bioactives in foods The commercial attractiveness of milk protein-based ingredients may be increased if the functionality of the films can be tailored to match the intended application. This requires an understanding of the relative importance of the various functionalities (e.g. barrier properties to specific components such as water and oxygen and mechanical properties that affect durability and cohesiveness) for preventing deteriorative reactions (e.g. due to loss of moisture or oxidation of food components) that limit the shelf-life of a product and/or increase visual appeal of products. The ability of milk protein films to serve other functions such as a being a carrier of antimicrobials, antioxidants or other nutraceuticals without significantly compromising the desirable primary barrier and mechanical properties of films will add value to the case for commercial use of these films. The ability to supply cost-effective functional milk protein-based film formulations in a convenient format to the end-user needs to be considered.
Milk Protein Film and
Coating Application Lab Executive summary The objective of this project is large-volume utilization of whey protein as a food coating or packaging material. To accomplish this, the following sub-objectives have been defined: 1. Develop whey protein coating formulations and processes to improve pilot-scale coating application efficiency, adhesion, durability and effectiveness of oxygen barrier and gloss coatings on peanut and chocolate surfaces, respectively. 2. Develop whey protein-lipid composite film systems that can be applied as moisture-barrier coatings to foods using pilot-scale coating equipment. Use data on the moisture barrier of the resulting composite films to predict effectiveness as coatings on dry foods and assess the prediction by performing analysis of the coated food. 3. Determine the diffusion characteristics and effectiveness of anti-microbial compounds in whey protein films and in cheese. Use this data to develop a mathematical model for predicting the effectiveness of anti-microbials contained in whey protein coatings on cheese. Assess the prediction with data on anti-microbial-carrying whey protein-coated cheese.
4. Determine effect of
moisture content and plasticizers on whey protein thermal transitions and then
use data to form films, first by thermal-compression-molding and then by
extrusion. Then, heat-seal these films into pouches for testing with milk
powders and other dry foods. Whey protein gloss-coating Edible coatings applied to the surfaces of foods can provide protection against biological, physical or chemical damage and extend the shelf-life of a product. Another benefit of edible coatings is that they can enhance the appearance of a product, making it more appealing to consumers. As well as being excellent oxygen and aroma barriers, whey protein coatings are transparent and glossy. These attributes can be used to create a shiny, smooth surface on the foods as well as protect foods from oxidative damage that would cause rancid off-notes in food flavors. A particular application for whey protein coatings is as an edible glaze on chocolate-covered peanuts. Of the many plasticizers tested, we have determined that WPI coatings formulated with sucrose as the plasticizer provide the highest level of gloss to confectionery products. We have also found that WPI:sucrose coatings adhere well to chocolate surfaces and are very durable.
It is
hypothesized that the slow gloss fade of WPI:sucrose coatings is linked to
crystallization of sucrose over time. To take advantage of the benefits (high
gloss, durability) of using sucrose at high concentration in WPI coatings, but
still keeping desirable attributes and quality, crystallization of sucrose in
whey protein coatings must be controlled. It has been determined that denatured
WPI hinders sucrose crystallization in films more than native WPI. It is
believed that the cross-linking between protein molecules that occurs during
denaturing creates a matrix that slows the crystallization process. The addition
of sucrose crystallization inhibitors to the WPI:sucrose coating formulations
further slows the transformation. We found that raffinose and a modified starch
were the better inhibitors and controlled sucrose crystallization. The rate of
crystallization is also affected by the relative humidity of storage conditions.
To better control sucrose crystallization in WPI/sucrose films and coatings and
hinder gloss fade, they should be stored in relative humidity environments lower
than 44 percent. Whey protein oxygen-barrier coatings Results showed that both the coating process and coating formulation play a significant role in the effectiveness of forming whey protein coatings on peanuts. It was found that if the coating pan were kept rotating as the coating solution was added and while peanuts dried in the pan, the area of the peanut surface that was coated increased. Increasing the amount of coating solution relative to the amount of peanuts significantly increased the coverage. WPC80 was found to be comparatively less effective than WPI in coating formulations. Lecithin, a natural surfactant, was also found to be a less effective compared to Span 20, a synthetic surfactant, in coating formulations. However, we believe that by adjusting the coating process, the advantages of using WPC80 and lecithin can be realized. Improvement of WPI-based oxygen-barrier coating coverage and adhesion on peanuts can be achieved by both modification of the peanut surface and optimization of the coating process. The surface of peanuts can be modified by addition of the natural surfactant lecithin to the WPI coating solution. The lecithin adsorbs to the peanut surface, with the result that the coating solution wets and spreads on the surface more easily. The peanut surface can also be modified by slight roughening. This also improves wetting and spreading of the WPI coating solution on the surface, as well as improving coating adhesion by mechanical interlocking into the roughened-surface grooves.
Investigation of the coating process indicates that temperature, WPI coating
solution addition rate, coating amount, drying fan speed and coating pan
rotation all affect WPI coating coverage and quality. Both sequential-batch
ladling of WPI-based coating solution and spray-coating can be used for coating
of peanuts. Whey protein-lipid composite moisture-barrier films
Several
techniques to WPI-lipid bilayer films were developed. A two-step bilayer film,
formed from molten beeswax coated onto a WPI base film, was the best moisture
barrier, with a water vapor permeability (WVP) two orders of magnitude less than
the WPI-only film. A one-step bilayer film, formed from separation of an
unstable emulsion, has a WVP only slightly lower that a WPI-only film. However,
heating this film above the melting point of the lipid lowers the WVP to half
that of the WPI-only film. Antimicrobial-containing whey-protein coating for cheese
Antimicrobial-containing whey protein coatings for preventing molding of cheese
show great potential. WPI coatings are easily formed on the surface of cheese.
Results show enhanced maintenance of preservative at the cheese surface (i.e.,
reduced preservative diffusion in films as compared to diffusion in American,
mozzarella, and Cheddar cheese). Further modification of the film formulation
has slowed diffusion of potassium sorbate and natamycin away from the cheese
surface. Potassium sorbate diffusion studies in Cheddar cheese have been
completed, and a mathematical model has been developed to determine the
shelf-life of coated Cheddar cheese. Using this diffusion data with new coating
techniques, antimicrobial WPI coatings could be applicable to other cheese
products such as shredded cheese. Furthermore, changes in the film composition
affect the diffusion characteristics of the film, allowing for adjustment of
these characteristics for other specific applications. The concept of
antimicrobial-containing whey protein coatings has the potential to optimize
preservative use and reduce cheese losses. Extrusion of whey protein films Transparent, flexible whey protein films can be made by thermal-compression molding. This is an important step toward forming whey protein films by the extrusion processes used for commercial synthetic films. The extrusion process is less time-consuming and a less expensive method for stand-alone whey protein film formation. Extruded whey protein films could be formed into pouches for milk powders and other dry foods and ingredients. Furthermore, the extrusion process could be used for applying extruded whey protein coatings on paper and plastic to provide grease- and oxygen-barriers to these materials, respectively. Differential scanning calorimetry (DSC) has been used to determine the thermal transition temperatures in whey protein-plasticizer mixtures. These temperatures are then used to extrude these mixtures into films. DSC results suggest that increasing the amount of glycerol will lower the extruder temperatures required to melt and soften the materials being extruded. Experiments with an extruder indicate that the best way of bringing together the appropriate amounts of whey protein and plasticizer in the extruder is to convey WPI powder as a dry feed with a gravimetric feeder and to pump glycerol as a liquid feed with a positive-displacement pump. The output of the extruder indicates that production of whey protein films is feasible. Experiments on heat sealing of whey protein films have shown that heat seals can be obtained that have adequate strength to form pouches capable of holding pre-measured amounts of milk powders and other dry ingredients for direct addition into food formulations.
UCD Dairy
Foods Technology Transfer Program (Technician) Executive summary The main objective of this project is to promote transfer of new concepts developed at UC Davis, involving value-added uses of milk components. We focused on concepts involving utilization of whey protein, in particular edible films and coatings. Our sub-objectives involve technology transfer efforts toward utilization of whey protein edible films as: 1. Oxygen-barrier coatings for nuts and other oxygen-sensitive food products 2. Glossy, moisture-resistant coatings for chocolate and other confectionery products
3. Grease and
oxygen-barrier coatings for paper Oxygen-barrier coatings for nuts and other oxygen-sensitive food products Whey protein isolate (WPI)-based films were compared to films made from other edible biopolymer materials. The materials studied included: WPI, soy protein isolate (SPI), aqueous shellac, starch and hydroxypropyl methylcellulose (HPMC). We compared the oxygen barrier properties of films with compositions that gave similar tensile (mechanical) properties (strength, flexibility, stretchiness and resilience). Glycerol-plasticized WPI films exhibited similar or greater tensile strength than the other biopolymers evaluated. WPI and SPI films with the same mass ratios of polymer to plasticizer had similar resilience (durability), and both WPI and SPI films were more resilient that the other materials. Although the resiliencies of WPI- and SPI-based films are similar, WPI films are more transparent and have less color and aroma compared to SPI films. The WPI, SPI and shellac films plasticized with glycerol were good oxygen barriers at 30 percent RH. However, again, WPI films excel when considering all attributes. Increasing plasticizer concentration in sucrose-plasticized SPI, starch, HPMC and shellac films resulted in a decrease in film stretchiness (elongation). However, for WPI films with a WPI:sucrose ratio = 1:3, the elongation increased dramatically to 151 percent. Thus, films with this particular formulation of WPI and sucrose exhibited excellent resiliency compared to the other biopolymer films. This suggests that WPI coatings made with this formulation would have better resistance to impact compared to other formulations. Sucrose-plasticized WPI, SPI and shellac films were all complete oxygen barriers when tested at 30 percent RH. The WPI films excel considering oxygen-barrier, tensile properties, transparency and color.
We have
established contact with a food manufacturer who is looking for a substitute
coating for their current shellac-based coating system. We provided samples of
their product that were coated with different formulations of our WPI-based
coatings. When subjected to heat stress testing, these samples held up at least
as well as shellac-coated samples. The appearance and heat tolerance of samples
coated with WPI-based coatings generated enough interest to prompt this company
to request a sufficient quantity of coating to conduct a plant trial. They also
requested pricing information and we provided a rough estimate of cost, based on
railcar loads of raw ingredients and labor costs. The company is ready to move
forward with additional evaluation as soon as whey protein coating formulations
are commercialized Glossy, moisture-resistant coatings for chocolate and other confectionery products Current practice in the confectionery industry involves application of an alcohol-based shellac coating (confectioner’s glaze) as a final step in the manufacturing of panned products. The shellac provides a moisture-resistant, glossy coating. However, alcohol-based shellac is hazardous because it is a very flammable solution. Also, during the drying process, volatile organic compounds (VOC’s) are released into the atmosphere, increasing air pollution. The EPA has limited VOC emissions allowable from the confectionery industry, prompting the need for a more environmentally and worker friendly glaze. Thus, our research has focused on developing water-based WPI coating solutions to be applied to confectionery products as a final glaze in the panning process. WPI films and coatings plasticized with sucrose have high gloss and durability. We coated chocolate-covered peanuts with this high gloss, durable, water-based WPI-sucrose coating formulation, for comparison with chocolate-covered peanuts that we coated with commercially available water-based coatings. For additional comparison, we also coated chocolate-covered peanuts with the industry standard, alcohol-based shellac. We evaluated all these coated products for initial gloss and gloss fade with time. WPI-coated chocolate had initial gloss quite close to alcohol-based shellac and similar or better than the other water-based coatings. Product coated with water-based shellac being marketed as a replacement for alcohol-based shellac did not appear glossy and had many tack marks. In addition, product coated with aqueous shellac has an undesirable flavor, and films made from this product become hazy as storage time increases or when exposed to moisture. Another noteworthy disadvantage is that the aqueous-based shellac was very difficult to remove from the panning unit during clean-up.
Upon
storage, the gloss of chocolate-covered peanuts coated with the WPI-sucrose
coating system slowly decreased, presumably due to sucrose crystallization. We
are presently testing concepts to inhibit sucrose crystallization and maintain
gloss over a longer period of time, with promising results. A controlled
temperature and relative humidity “coating room” has been established to conduct
these studies. In addition to this development work, we are making additional
industrial contacts that will help with technology transfer of our coating
systems. Grease and oxygen-barrier coatings for paper The production of WPC-based coating formulas has been scaled up to gallon-sized batches that will be needed for a mini-production trial at a paper-coating plant. The grease-barrier properties of these coatings were found to be as good as coatings produced using smaller experimental quantities as measured by a standard method. Refrigeration and freezing have been evaluated for improving the storage stability of WPC coating solution. It is possible to freeze a sample for a short period of time and then store it at refrigerated temperatures before use without changing properties. This is a good solution for providing coating samples for testing to industry, until an appropriate heat processing method for producing a shelf-stable product can be established. Another alternative is supplying the WPC coating formulation as a dry mix. Some paper-coating suppliers provide biopolymer-based coatings as a dry mix that is hydrated and prepared within the paper processing plant. Thus, this means of providing the coating system will also be investigated.
The UC
Davis Dairy Foods Technology Transfer Program promotes the exposure and transfer
of technology developed in the Edible Films Group involving value-added uses of
milk components for industrial applications. Oxygen-barrier coatings for nuts and other oxygen-sensitive food products WPI-based films compared quite favorably to soy protein, starch, HPMC and shellac coating systems that are commercially available. Glycerol- and sucrose-plasticized WPI films are equal or better oxygen barriers, compared to other films with similar mechanical properties made from these other biopolymers. In addition, WPI films have desirable transparency and no color or aroma. Depending on the plasticizer concentration in the film formulation, denatured WPI –based films can be customized to exploit oxygen-barrier properties, glossiness and mechanical properties. This information can be used to convince potential users of the advantages of whey protein films and coatings over other materials.
A yogurt-coated snack food coated with different WPI-based formulations was at least as glossy as a shellac-coated product. Coating formulations with higher sucrose concentrations show higher initial gloss values than other WPI-based formulations or shellac-coated product. Control of temperature and relative humidity (RH) during coating application and subsequent coating storage studies is critical to understanding factors that contribute to gloss. Thus, a room with controlled temperature and RH for coating and product storage was established to explore optimization of coating gloss.
Chocolate-covered peanuts coated with WPI:sucrose showed high initial gloss,
similar to shellac. At low relative humidities, WPI-based coating systems
maintained gloss for extended periods. However, at higher relative humidities,
gloss fade proceeded slowly. Including small amounts of other sugars as
additives appears to inhibit the sucrose crystallization that causes the gloss
fade. Grease and oxygen-barrier coatings for paper Results show that the shelf-life of WPC-based paper-coating solutions can be extended through a combination of frozen and refrigerated storage, without affecting coating performance. Commercial sterilization of the WPC coating solutions using UHT processing should be evaluated and the shelf life and performance of coatings subjected to this type of processing evaluated. Another approach that merits evaluation is making a dry mix that is hydrated by the user just before the coating of paper. |
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