Sensory directed determination of odor important components of natural (raw) and roasted pecan oil

Malloy, Kristen Lynn

Permalink

https://hdl.handle.net/2142/127441 Copy

Description

Title

Sensory directed determination of odor important components of natural (raw) and roasted pecan oil

Author(s)

Malloy, Kristen Lynn

Issue Date

2024-09-27

Director of Research (if dissertation) or Advisor (if thesis)

Cadwallader, Keith

Committee Member(s)

• Engeseth, Nicki
• Miller, Michael

Department of Study

Food Science & Human Nutrition

Discipline

Food Science & Human Nutrition

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• pecan
• pecan oil
• aroma
• flavor
• volatile profile
• sensory descriptive analysis
• aroma profile
• roasted pecan oil
• roasted pecan
• aroma analysis
• analytical

Abstract

Since their discovery, pecans have been enjoyed as a nutritious and flavorful snack, eventually staking their claim as a cherished baking ingredient with notable desserts including the pecan pie and the pecan praline. The utility of the pecan has been further expanded in recent years with the emergence of “gourmet specialty oils” popularized for their impressive nutritional profiles and bold flavors. Gourmet specialty oils largely consist of virgin, cold-pressed tree nut oils (often made from the roasted form of the nut) which retain their beneficial micro and macronutrient profiles and unique aromas as a result of the gentle production processes used. Roasted pecan oil is a specialty oil that has made its way onto the market in recent years, standing out against commodity oils from a health and flavor perspective. With its rising popularity, studies investigating the flavor profile of roasted pecan oil could prove to be useful. The purpose of this study was to qualitatively and quantitatively analyze the aroma profile of natural (raw) pecan oil and roasted pecan oil using sensory descriptive analysis followed by instrumental aroma analysis to determine how the perceived aroma profile of pecan oil transforms with roasting of the kernel (prior to oil extraction). Sensory descriptive analysis was conducted to determine the predominant perceived aroma attributes and their intensities in natural (raw) and roasted pecan oils (made from kernels roasted for 5, 10, 15, and 20 minutes at 350 °F ≈ 175 °C). The sensory attribute scores were also used to determine an optimal roasting time to use for instrumental aroma analysis. Volatiles were extracted from the oil samples using solvent-assisted flavor evaporation (SAFE), and odor activity was determined by gas chromatography-olfactometry (GC-O) and aroma extract dilution analysis (AEDA). Selected odorants were subsequently identified and quantified by gas chromatography-triple quadrupole-mass spectrometry [GC-(TQ)MS] using stable isotope dilution analysis (SIDA). Sensory descriptive analysis generated 10 predominant aroma attributes in raw and roasted pecan oils: roasty, nutty, malty, caramel, buttery, doughy, grassy, oily, rancid, and burnt. Intensity ratings for these attributes revealed that the aroma profile of roasted pecan oil is optimal with about 15 minutes of roasting at 350 °F (≈175 °C), with this sample receiving significantly higher intensity scores compared to the other roasted samples for positive attributes including roasty, nutty, malty, caramel, and buttery (with the exception of the 20-minute roasted sample being highest for the roasty attribute), and intensity scores remaining low for negative attributes including grassy, rancid, and oily. These results helped select 15 minutes as the roasting time to use for instrumental aroma analysis. GC-O analysis detected 77 odorants with flavor dilution (FD) factors ranging from < 3 to 729 in roasted pecan oil (RPO), and 44 odorants with FD factors ranging from < 3 to 27 in natural (raw) pecan oil (NPO). Of the total 77 odorants detected, 61 were positively identified, 10 were tentatively identified, and 6 remain unknown. Of the positively identified odorants, 54 were quantitated in RPO and 36 in NPO. Additionally, 8 volatile compounds that were not detected by GC-O but could be detected by gas chromatography-mass spectrometry (GC-MS) were quantitated in RPO (not detected in NPO) as they could possibly provide some insight into the chemistry that occurs within the pecan during roasting. Following quantitation, odor activity values (OAVs) were calculated to determine the odor impact of the selected odorants. These results revealed 28 compounds with odor importance in RPO (OAV ≥ 1): 2,3-pentanedione, 2-acetyl-1-pyrroline, 2-methylpropanal, 3-methylbutanal, (E,Z)-2,4-decadienal, 2-propionyl-1-pyrroline, 4-hydroxy-2,5-dimethyl-3-(2H)-furanone (HDMF), 2-methylbutanal, 2,3-diethyl-5-methylpyrazine, 2-acetyl-1,4,5,6-tetrahydropyridine, (E,E)-2,4-decadienal, acetic acid, 3-(methylthio)propanal (methional), 1-octen-3-one, 2-ethyl-3,5-dimethylpyrazine, dimethyl trisulfide, phenylacetaldehyde, 2,3-butanedione, octanal, trans-4,5-epoxy-(E)-2-decenal, 2-acetylpyrazine, hexanal, 2-methoxy-4-vinylphenol (PVG), 2-pentylpyridine, 2-acetyl-2-thiazoline, 2-methyl-3-(methyldithio)furan (MT-MFT), (E,E)-2,4-nonaidenal, and γ-dodecalactone. Determination of OAVs revealed NPO had a much lower odor impact, with just 3 odorants with significant odor activity (OAV ≥ 1): acetic acid, methional, and HDMF. Analysis of OAVs revealed a correlation between sensory and instrumental analyses. According to GC-O, the compounds with the greatest odor impact in terms of OAV possessed roasty, popcorn-like, nutty, malty, caramel-like, buttery, fatty, green, and grassy aromas, all of which can be related to the terms generated by the panel during sensory descriptive analysis including roasty, nutty, malty, caramel, buttery, grassy, oily, and rancid. Overall, this study is the first of its kind to analyze the volatile aroma profile of natural (raw) and roasted pecan oils by both sensory and instrumental aroma analysis. Of the odor-active compounds detected, 35 are unique to this study as they have not been previously reported in studies related to the flavor chemistry of pecan products. The results of this study highlight the importance of heterocyclic volatiles such as pyrazines, pyrrolines, furanones, and lactones that possess nutty, popcorn-like, caramel-like, and creamy, coconut-like aromas, as well as volatile aldehydes and ketones that possess malty and buttery aromas in RPO, all of which can be attributed to the reactions occurring within the pecan as a result of heat treatment, namely the Maillard reaction and Strecker degradation. The importance of these reactions for volatile formation in roasted pecans is also supported by the absence of these compounds in NPO, demonstrating that roasting is necessary to form these volatiles that give roasted pecan oil its characteristic aroma.

Graduation Semester

2024-12

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/127441

Copyright and License Information

© 2024 Kristen Lynn Malloy

Owning Collections