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Table 3. Compounds Responsible for Specific Flavors in Oxidized Fats

Flavor Source compound(s)

Cardboard Non-irares-2,-irares-6-dienal

Oily Aldehydes

Painty Pent-2-enal, aldehydes

Fishy Deca-iraras-2,cis-4,frans-7,trienol, oct-l-en-3-one

Grassy 7>an.s-hex-2-enal, nona-2,6-dienal

Deep-fried Deca-imres-2,ira/is-4-dienal

Table 4. Sensory Evaluation of Oil

Flavor score Description of flavor

10 Completely bland

9 (good) Trace of flavor, but not recognizable

8 Nutty, sweet, bacony, buttery

7 (fair) Beany, hydrogenated

6 Raw, oxidized, musty, weedy, burnt, grassy

5 (poor) Reverted, rubbery, butter

4 Rancid, painty 3 (very poor) Fishy, buggy

2 Intensive flavor and objectionable

1 (repulsive)

pared with sensory evaluation, gas chromatography has many advantages including rapid analysis time, convenience, low cost, and high reproducibility. A preliminary gas chromatographic analysis of flavor compounds of mayonnaise has been done to predict the sensory quality of mayonnaise during storage (37). Various flavor compounds have been identified in mayonnaise including allyl isothio-cyanate, acetic acid, ethyl acetate, pentane, and isomers of 2,4-decadienal. As storage time increased, levels of pentane and 2,4-decadienal increased, whereas other volatile concentrations stayed the same. The flavor compound allyl isothiocyanate, the major flavor constituent of mustard, and acetic acid and ethyl acetate, the flavor compounds in vinegar, did not change during the six-month storage period. There was a correlation coefficient of greater than 0.9 between actual sensory scores of mayonnaise and predicted sensory scores by gas chromatography. Therefore, the shelf life of mayonnaise can be accurately predicted by analyzing specific compounds associated with off-flavors such as pentane and 2,4-decadienal during storage periods.

Gas chromatography can also be used to study the effects of storage conditions and processing methods on the oxidation of fats and oils. Soybean and corn oils were exposed to different periods of light to produce a wide range of flavor quality (38). As the period of light storage increased, the amount of 2,4-decadienal (as measured by gas chromatography) increased and the sensory scores decreased. The correlation of sensory evaluation and instrumental analysis using gas chromatography was greater than 0.95.

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