Aroma-active and off-flavor compounds of nonfat dried milk

Application of aroma extract dilution analysis (AEDA) on the volatile components of low, medium and high heat-treated nonfat dry milks (NDM) revealed aroma-active compounds in the log₃ flavor dilution (log₃ FD) factor range of 1 to 7. The following compounds contributed the highest log₃ FD factors to overall skim milk powder flavor: 2,5-dimethyl-4-hydroxy-3(2H)-furanone [(Furaneol®), burnt sugar-like]; butanoic acid (rancid, cheese-like); 3-(methylthio)propanal [(methional), boiled potato-like]; o-aminoacetophenone (grape-like, foxy); δ-decalactone (sweet, fatty); pentanoic acid (sweaty); 4,5-dimethyl-3-hydroxy-2(5H)-furanone [(sotolon), curry, caramel-like]; 3-methoxy-4-hydroxybenzaldehyde [(vanillin), vanilla, waffle-like]; 2-acetyl-l-pyrroline and 2-acetyl-2-thiazoline (popcorn-like); hexanoic acid (vinegar-like); phenylacetic acid (rose-like); octanoic acid (waxy); nonanal (fatty, stale); and 1-octen-3-one (mushroom-like). The odor intensities of butanoic acid and Furaneol® were not influenced by heat treatment, but pentanoic acid had higher odor intensities in high-heat skim milk powder than in low-heat powders in acidic fractions. A similar trend was observed for the neutral/basic components, methional and o-aminoacetophenone; however, the odor intensities of 2-acetyl-1-pyrroline and 2-acetyl-2-thiazoline were not affected by heat treatment. Sensory evaluation results also indicated that heat generated compounds and some lipid oxidation products have the major impact on the flavor profile of NDM.; The contributors of off-flavors were also investigated. A variety of aldehydes, ketones, free fatty acids, and alcohols were responsible for undesirable flavors of NDM. The following off-flavor compounds exhibited high aroma impact by AEDA: 3-(methylthio)propanal (potato/brothy); o-aminoacetophenone (grape/foxy); 2,5-dimethyl-4-hydroxy-3(2H)-furanone and 2-methyl-3-hydroxy-4H-pyran-4-one (burnt sugar/caramel); butanoic acid (rancid/cheesy), acetic, and hexanoic acids (sour); octanoic, decanoic, and dodecanoic acids (waxy); p-cresol and 3-methylindole (fecal); dimethyl trisulfide (cabbage); (E,E)-2,4-decadienal (fried fatty); furfuryl alcohol (rubber); phenylacetic acid (rose-like); and 1-octen-3-ol (mushroom).