Stabilization of the Potent Odorant 2-Acetyl-1-pyrroline and Structural Analogues by Complexation with Zinc Halides

Abstract

2-Acetyl-1-pyrroline (2AP) and the structurally similar compounds 6-acetyl-2,3,4,5-tetrahydropyridine (ATHP, along with its tautomer 6-acetyl-1,2,3,4-tetrahydropyridine), 2-propionyl-1-pyrroline (2PP), and 2-acetyl-2-thiazoline (2A2T) are well-known potent odorants in various food products. However, due to the highly unstable nature of these compounds, especially 2AP and ATHP, they are scarcely used commercially in flavor formulations. A novel and attractive method for the stabilization of these potent odorants in dry powder form is presented. Coordination of 2AP, ATHP, 2PP, and 2A2T to zinc ions (ZnI2, ZnBr2, or ZnCl2) resulted in the formation in high yields of stable crystalline complexes, which upon hydration release the free odorant. Infrared spectroscopy was used to study the coordination complexes. 2AP contains donor atoms, which coordinate (with covalent character) through both the heterocyclic nitrogen and carbonyl oxygen atoms to the zinc ion. This is also the case for ATHP and 2PP, but not for 2A2T, because the sulfur group in 2A2T provides a third possible donor site. Stability studies showed that the 2AP-ZnI2 complex (with 14% loading) maintained >94% retention of 2AP after 3 months of storage at ambient temperature in a dry environment. Meanwhile, the ATHP-ZnI2 complex was similarly stable and retained 89% of the ATHP after 3 months of storage. This stabilization technology may enable the commercial use of this powerful aroma compound as a flavoring agent.

Evaluation of 2-acetyl-1-pyrroline in foods, with an emphasis on rice flavour

“…Unfortunately, 2-acetyl-1-pyrroline has limited stability. Pure 2-AP will turn red and degrade within 10 min at room temperature (Fang & Cadwallader, 2014). This instability of 2-AP was noticed when it was first identified by Buttery et al (1982), and this instability was assumed to be due to polymerisation.…”

“…Gum acacia and/or starch mixed materials were used in a patented form by Srinivas, Sulochanamma, Raghavan, and Gurudutt (2006), to form a stable 2-AP powder using spray drying, but the stability of this powder was not reported. Fang and Cadwallader (2014) recently reported a novel stabilisation method, using zinc ions to solve 2-AP powder storage problems. Anhydrous 2-AP and ZnI2 were added into diethyl ether to form a yellowish precipitate, which was the desired 2-AP-ZnI2 complex.…”

“…Therefore, it may be necessary to combine this technique with an encapsulation technique to protect the 2-AP-zinc halide complex in a changeable food environment (Fang & Cadwallader, 2014).…”

“…Although there is a high commercial interest in 2-AP because of its desirable sensory attributes, the instability of this compound is a significant problem for its commercial application. Pure 2-AP will turn red and degrade within 10 minutes at room temperature (Fang & Cadwallader, 2014), and there is significant short-term reduction of 2-AP concentration in food products, such as popcorn (Schieberle, 1995) and raw fragrant rice (Widjaja, Craske, & Wootton, 1996a).…”

Silver Colloid and Silver Mirror Complex as Surface Enhanced Raman Substrate for Volatile Organic Compounds Analysis

“…The volatile compound is also used in agricultural product of Thailand such as Kao Hom Mali and Kao Hom Prathumtani. They have identical appearance and same volatile compounds as 2-Acetyl-2-thiazoline.2-Acetyl-2-thiazoline is also important aroma compound identified in cooked rice, beef flavor, and another food flavor 7,[12][13] . Further more, Toluene is the index of contamination in food industry.…”