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Journal ArticleDOI

Soy Protein Fortification of a Low‐fat Dairy‐based Ice Cream

01 Nov 2003-Journal of Food Science (John Wiley & Sons, Ltd)-Vol. 68, Iss: 9, pp 2651-2657

AbstractThe flavor and texture effects of soy protein fortification of low-fat dairy-based ice cream were characterized. Low-fat ice cream mixes were formulated with 0%, 2%, and 4% soy protein isolate (SPI). Sensory attributes, volatile flavor components, instrumental color, and viscosity were compared. SPI-fortified mixes displayed different textural and color properties compared with the 0% SPI control. Green/grassy and doughy/fatty flavors increased in intensity with added SPI. Instrumental volatile analysis revealed higher intensities of hexanal, (Z)-4-heptanal, 2-acetyl-1-pyrroline, and (E,E)-2,4-decadienal in the SPI-fortified mixes compared with controls. This information will aid in the design and optimization of an acceptable soy-fortified dairy ice cream. Keywords: soy protein isolate, ice cream, low-fat, flavor, volatile analysis

Topics: Soy protein (55%), Flavor (52%)

Summary (4 min read)

Introduction

  • Soybeans have served as a major source of dietary protein for many people throughout Asia for over 1,000 years.
  • Though this market has enormous growth, there still remains a major problem in expanding the use of soy protein, its characteristic “beany”, grassy, and bitter flavors (Kinsella 1979).
  • Trans-2, 4-decadienal was found to be a major odor contributor to the oxidized, fatty off-aroma of SPI (Boatright and Lei 1999).
  • Drake and others (2000; 2001) evaluated soy protein fortification of dairy yogurts.
  • The frozen treats market has been and continues to be a leading, high gross food market, representing nearly $ 7 billion or 26% of the total frozen food sales in grocery stores (Anonymous 2002a).

Soybean History

  • The soybean is widely believed to have originated 4000-5000 years ago in the north and central regions of China (Liu 1997a).
  • Soybeans have been consumed throughout Asia for more than 1000 years in a variety of traditional soyfood products.
  • In the process of solvent extraction, defatted “white” flakes intended for food use are processed by flash solvent-removing systems which incorporate heat and vacuum to remove residual solvent (Lusas and Riaz 1995; Soy Protein Council 1987).
  • Edible soybean proteins are used primarily as secondary ingredients in a variety of processed foods (Mounts and others 1987).
  • Kirk and others (1998) designed a study to determine if isoflavones in soy protein isolate confer protection from atherosclerosis, reduce total plasma cholesterol levels and protect against lipoprotein oxidation in atherosclerosis-susceptible mice.

Soy and Functional Foods

  • Recently, the food industry has seen expansive growth in what is known as “functional food”.
  • Recent growth of functional foods far outpace that of conventional foods and supplements, and has attracted the interests of both consumers and food producers (van Poppel 1998) (Locklear 1999).
  • Soy represents a considerable market with high margins and growth rates, educated customers, premium pricing, and a healthy food platform (Tischler 2002).
  • This process allows for both concentration and transfer of flavor compounds to a nonpolar solvent for analysis (Reineccius 1999).
  • The technique of GC/O allows both flavor chemists and sensory scientists a method of chemical analysis that provides sensory responses to odoractive chromatographically separated chemicals.

Sensory Analysis of Flavor

  • Chemical flavor compounds contribute to flavors and aromas and greatly affect the overall perception of a particular food or ingredient.
  • Descriptive analysis is considered to be the most comprehensive and informative sensory evaluation tool, with information from tests that can be applied to consumer acceptance information and instrumental measures by means of such statistical techniques as regression and correlation.
  • As well, the nine-point hedonic scale may provide the opportunity to explore for more complex information having to do with an individual’s reason for liking or disliking a product (Lawless & Heymann 1998).
  • While training of profile panels requires time and a high degree of member motivation and interest, a panel can provide thorough and reliable descriptions of products in a short time (Larmond 1976).
  • There is also an inferential function of statistics, which can provide some kind of confidence or support for conclusions made about the products and variables that are being tested.

Flavor Compounds in Soy Protein

  • Through the utilization of various techniques, many flavor and aroma components have been identified as contributing to the flavor of soy and soy protein products.
  • In the identification of compounds contributing to 34 undesirable flavors in SPI, 2-pentyl pyridine was found to be a major contributor of the characteristically throat catching and grassy flavor along with a fishy odor (Boatright and Crum 1997).
  • Sensory Aspects of Soy A major problem in expanding the use of soy has been its characteristic “beany”, grassy, and bitter flavors (Kinsella 1979).
  • The study utilized soy flour (SF), soy protein concentrate (SPC) and soy protein isolate (SPI) at varying percentages in place of non-fat milk solids in vanilla soft-serve frozen dessert formulas.
  • Flavor and odor of the soft-serve dessert formulas were evaluated along with other characteristics by an eight-member, in-house panel of judges over a period of five months.

Soy Protein Fortification of a Low Fat Dairy-Based Ice Cream

  • Kristofer G. Friedeck, Yonca Karagul-Yuceer, MaryAnne Drake1 1Department of Food Science, North Carolina State University, Box 7624, Raleigh, NC 27695 53 Abstract.
  • Though this market has enormous growth, there still remains a major problem in expanding the use of soy protein, its characteristic “beany”, grassy, and bitter flavors (Kinsella 1979).
  • Trans-2, 4-decadienal was found to be a major odor contributor to the oxidized, fatty off-aroma of SPI (Boatright and Lei 1999).
  • Materials and Methods Soy Protein Isolate and Low fat ice cream mixes Prior to initiating experiments, several commercial SPIs (5) were received and screened for overall flavor profiles in low fat ice cream mix, and the presence of soyassociated off flavors.

Physical Measurements

  • Differences in viscosity were observed across a shear rate increase from 1 to 100 s-1, with the SPI fortified mixes exhibiting significantly higher viscosities than that of the control at the lowest (1 s-1) and highest (100 s-1) shear rate (Table 2).
  • The 4% SPI mix had a significantly lower L* value (76.40) than the 0% control (80.22), indicating ice cream mix fortified with SPI was less white in comparison to that of a typical low-fat ice cream (Table 3).
  • Values for a*, which signify red (+) and green (-), were also significantly different among treatments.
  • The b* value for the control increased with increasing levels of SPI, which demonstrates that the mixes increased from blue to yellow in color with increased SPI.

Sensory Evaluation

  • Nine trained panelists were selected based on interest, time available, and knowledge of dairy associated flavors.
  • Flavor and texture terms identified and selected by the panelists are listed in Table 1.
  • 59 Panelists scored responses on 15-point numerical intensity scales anchored on the left with “none” and on the right with “very”, and “light” on the left and “dark” on the right for color.
  • Descriptive analysis was conducted by each panelist in triplicate on duplicate batches in a randomized block design for control (0%), 2, and 4% SPI fortified low fat ice cream mixes (Meilgaard and others 1999).
  • Samples (30 g) were served in 59-ml plastic cups fitted with plastic lids (Sweetheart Cup Co., Owings Mills, MD) and labeled with three digit codes.

Volatile Flavor Components

  • High Vacuum Distillation Glassware used in high vacuum transfer (HVT) was baked at 160 ºC for at least two hours prior to use.
  • A rough pump/diffusion pump vacuum source, fitted with a receiving tube and waste tube was connected to the sample flask.
  • The acidic compoundcontaining solvent phase was drawn off of the aqueous phase and collected after each wash, followed by drying and concentrating, as was carried out for the neutral/basic phase.
  • The system consisted of an HP5890 Series II GC/HP 5972 mass selective detector (MSD, Hewlett-Packard, Co.).
  • Tentative identifications were based on comparison of the mass spectra of unknown compounds with those in the National Institute of Standards and Technology (NIST 1992) mass spectral database or on the matching of RI values and odor properties of unknowns to those of authentic standards.

Mix Composition

  • Vanilla and chocolate flavored low fat ice creams were prepared with 0 and 4% SPI added in 113.6 L batches.
  • A fortification level of 4% SPI was chosen for consumer acceptance testing for the reason that it contained a significant amount of soy protein (2.64g / 66g serving) to qualify as a “good source” of soy protein, whereas the 2% SPI formula did not.
  • Pressures were 12.4 and 3.4 MPa for the first and second stages, respectively.
  • Chocolate flavoring (#15114, David Michael & Co., Philadelphia, PA) was also added to the chocolate mixes prior to freezing at a usage rate of 0.20% w/w.

Consumer acceptance testing

  • Consumer evaluation of ice cream was approved by the university institutional review board.
  • Faculty, staff, and students of the university community participated in the study.
  • Ice creams were evaluated one week after manufacture.
  • Cups were labeled with random three-digit codes.
  • Consumers were also asked a question in order indicate purchase intent of a low fat soy fortified ice cream.

Statistical Analysis

  • Statistical analysis of viscosity, color, descriptive and consumer sensory data were evaluated by analysis of variance (PROC GLM) with means separation.
  • Significantly different means (P<0.05) were separated using least square means.
  • Demographic data was 67 evaluated by frequency distribution with chi square tests (PROC FREQ) (SAS version 8.2, Cary, NC).

Descriptive Sensory Analysis

  • Descriptive analysis showed significant differences among treatments for flavor and textural characteristics (Table 4).
  • Low fat ice cream mixes would be expected to have sweet taste and delicate dairy-associated flavors.
  • Sweet taste and sweet aromatic were the highest perceived flavor associated attributes among all mixes.
  • The highest intensities of green/grassy and doughy/fatty were noted in the 4% SPI fortified mixes.
  • Sensory-perceived textural and color differences were also observed.

Volatile Flavor Analysis

  • Internal standard recovery was consistent between treatments and individual treatment replications, as determined by relative abundance.
  • Control mixes were characterized by lower overall intensities of aroma-active compounds, while the SPI fortified mixes exhibited higher overall intensities of compounds including aldehydes, lactones, and some heat generated compounds.
  • Hexanal was positively identified by GCO and GC-MS in all low fat ice cream mixes.
  • It is although notable that the highest intensity of green aromatic detected by GCO (Table 5) and sensory evaluation (Table 4) was observed in the 4% SPI mix.
  • 70 (Z)-4-heptenal, a compound with an aroma described as “doughy”, “fishy”, and (E,E)-2,4-decadienal (doughy/fatty) have also both been shown to be volatile components of both milk and soy products (Karagul-Yuceer and others 2001; Boatright and Crum 1997).

Flavored ice cream mixes

  • Consumer acceptance of low fat ice cream with and with out SPI Consumers detected no significant differences in appearance or overall texture liking among the chocolate and vanilla ice creams (Table 7).
  • Characteristics, Nutritional Aspects, and Utilization, also known as Soy Protein Products.

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Abstract
FRIEDECK, KRISTOFER GREGG. Soy Protein Fortification of a Low Fat Dairy-
Based Ice Cream. (Under the direction of Dr. MaryAnne Drake.)
Since the inception of the 1998 FDA approved health claims linking soy and
health, soy protein has been investigated as a potential ingredient in many foods.
Products containing soy protein have been characterized as having beany or woody off-
flavors, which are unacceptable to many American consumers. Frozen dairy dessert
products, in comparison, are appealing to many consumers and may potentially serve as
carriers for functional ingredients such as soy protein. Understanding the flavor and
sensory impact of soy protein in a dairy-based frozen dessert is important in designing
soy fortified dairy products with high market acceptability. The goals of this research are
to identify and characterize aroma active compounds contributing to off flavors in soy
protein fortified dairy-based frozen desserts, and assess associated sensory impacts.
Descriptive sensory analysis was conducted on frozen dairy dessert mixes
formulated with 0, 2, and 4% soy protein isolate (SPI). Duplicate samples (750g)
containing an internal standard were distilled by high vacuum transfer followed by
extraction of the distillate with diethyl ether. Extracts containing volatile compounds
were separated into neutral-basic and acidic fractions and analyzed by gas
chromatography-mass spectroscopy (GC-MS) and gas chromatography-olfactometry
(GC-O) and aroma extract dilution analysis (AEDA). Comparison of retention indices,
odor properties, and GC-MS data against reference standards was performed for
identification of compounds. SPI fortified dessert mixes displayed different textural and
color properties in comparison to the 0 % SPI control. Soy fortification increased mouth

viscosity and mouthcoating. Green/grassy and doughy/fatty flavors increased in intensity
with added SPI. GC-O analysis revealed higher concentrations of hexanal (green), (Z)-4-
heptanal (fishy/oily), 2-acetyl-1-pyrroline (nutty/popcorn), and (E,E)-2,4-decadienal
(fatty/frier oil) in the SPI fortified samples compared to controls. Consumer testing
revealed lower acceptability of SPI fortified ice creams in conjunction with lower
intensities of pleasing ice cream flavors with added SPI. Chocolate flavored SPI fortified
ice creams received higher acceptability scores than vanilla flavored SPI fortified ice
creams. Consumers indicated a general knowledge of the healthfulness of low fat dairy
desserts and soy foods. This information will aid in the design and optimization of an
acceptable soy fortified low fat dairy ice cream.


ii
Biography
Kristofer Gregg Friedeck was born on January 4, 1975, in Seguin, Texas to
Walter and Jan Friedeck. His family also includes his wife Melanie, and sister, Michelle.
Kristofer graduated from Southwest Texas State University in August, 2000 with
a Bachelor of Science degree in Nutrition and Foods. Kristofer began work in Houston
Texas at H.E.B. Grocery Company in November 2000 where he worked as a Chef. He
left H.E.B. in April 2001 to pursue a Master of Science degree in Food Science at North
Carolina State University.

iii
Acknowledgments
The author would like to express his appreciation for the support and
encouragement provided by his wife, family, friends, laboratory colleagues, and major
advisor.
The author is thankful to Yonca Karagul for all of her expertise, technical
assistance, and patience. Also appreciation is given to Jamie Parker and Mary Whetstine
for all of their help, friendship, and mutual folly. Dr Mary Anne Drake deserves many
thanks for her role as a major advisor and mentor.
Particular thanks is given to the Food Science department faculty, staff, and
students at NCSU, who were so warm and welcoming, and always eager to lend a hand
whenever the need arose.
Most deserving of credit for the completion of this degree are the author’s family.
This endeavor was greatly facilitated by their continuous support and encouragement.
Immense gratitude is expressed toward Melanie for her immeasurable love, commitment,
and strength during completion of this degree.

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Since the inception of the 1998 FDA approved health claims linking soy and health, soy protein has been investigated as a potential ingredient in many foods. The goals of this research are to identify and characterize aroma active compounds contributing to off flavors in soy protein fortified dairy-based frozen desserts, and assess associated sensory impacts. Frozen dairy dessert products, in comparison, are appealing to many consumers and may potentially serve as carriers for functional ingredients such as soy protein.