Identification of Candidate Amino Acids Involved in the Formation of Blue Pigments in Crushed Garlic Cloves (Allium sativum L.)

ABSTRACT:  The color-forming ability of amino acids with thiosulfinate in crushed garlic was investigated. We developed reaction systems for generating pure blue pigments using extracted thiosulfinate from crushed garlic and onion and all 22 amino acids. Each amino acid was reacted with thiosulfinate solution and was then incubated at 60 °C for 3 h to generate pigments. Unknown blue pigments, responsible for discoloration in crushed garlic cloves ( Allium sativum L.), were separated and tentatively characterized using high-performance liquid chromatography (HPLC) and a diode array detector ranging between 200 and 700 nm. Blue pigment solutions exhibited 2 maximal absorbance peaks at 440 nm and 580 nm, corresponding to yellow and blue, respectively, with different retention times. Our findings indicated that green discoloration is created by the combination of yellow and blue pigments. Eight naturally occurring blue pigments were separated from discolored garlic extracts using HPLC at 580 nm. This suggests that garlic discoloration is not caused by only 1 blue pigment, as reported earlier, but by as many as 8 pigments. Overall, free amino acids that formed blue pigment when reacted with thiosulfinate were glycine, arginine, lysine, serine, alanine, aspartic acid, asparagine, glutamic acid, and tyrosine. Arginine, asparagine, and glutamine had spectra that were more similar to naturally greened garlic extract.     

Identification of candidate amino acids involved in the formation of pink-red pigments in onion (Allium cepa L.) juice and separation by HPLC

The formation of pink-red pigments ("pinking") by various amino acids was investigated by reacting amino acids with compounds present in onion juice. The unknown pink-red pigments were generated and separated using high-performance liquid chromatography (HPLC) and a diode array detector (DAD) in the range of 200 to 700 nm. To generate pink-red pigments, we developed several reaction systems using garlic alliinase, purified 1-propenyl-L-cysteine sulfoxide (1-PeCSO), onion thiosulfinate, natural onion juice, and 21 free amino acids. The compound 1-PeCSO was a key compound associated with pinking in the presence of both the alliinase and amino acids. Numerous naturally occurring pink-red pigments were detected and separated from pink onion juice using the HPLC-DAD system at 515 nm. Most free amino acids, with the exceptions of histidine, serine, and cysteine, formed various pink-red pigments when reacted with onion thiosulfinate. This observation indicated that onion pinking is caused not by a single pigment, but by many. Furthermore, more than one color compound could be produced from a single amino acid; this explains, in part, why there were many pink-red compound peaks in the chromatogram of discolored natural onion juice. We presumed that the complexity of the pink-red pigments was due to the involvement of more than 21 natural amino acids as well as several derivatives of the color products produced from each amino acid. We observed that the pinking process in onion juice is very similar to that of the greening process in crushed garlic, emphasizing that both thiosulfinate from flavor precursors and free amino acids are absolutely required for the discoloration.     

大蒜中硫代亚磺酸酯提取工艺及其稳定性研究

采用乙醇溶液提取大蒜中的硫代亚磺酸酯,研究了乙醇浓度、提取温度、提取时间、料液比对硫代亚磺酸酯提取量的影响,在单因素实验的基础上采用响应面法确定了最佳提取条件:乙醇浓度为64.89%,提取温度为19.06℃,提取时间为1.48 h,料液比为1∶4.48(g∶mL),硫代亚磺酸酯含量可达4.17 mmol/100 g。对硫代亚磺酸酯的稳定性研究表明:随着温度的升高,硫代亚磺酸酯稳定性下降,提取液在贮存过程中,随着硫代亚磺酸酯含量的降低,二烯丙基二硫醚(DADS)与二烯丙基三硫醚(DATS)的含量会上升。     

提高冻干香葱品质的工艺研究

为保持真空冷冻干燥香葱的鲜绿、天然的葱香味及品质,采用漂烫和护色剂对香葱进行浸泡护色处理,固相微萃取气质联用(SPME-GC-MS)测定香葱的挥发性成分,并确定真空冷冻干燥香葱气味最浓郁时的干燥时间、温度和真空度。实验表明:SPME-GC-MS分析确定以硫代亚磺酸酯的含量来衡量干燥后香葱气味的浓郁程度。干燥香葱颜色最鲜亮时的条件为:100℃水中烫漂30s,0.3%碳酸钠碱液中浸泡10min,0.03%氯化锌和0.2%氯化钙护绿液中护色30min。满足香葱香味最浓郁及水分要求的条件为:0℃下升华干燥6h,25℃下解析干燥2h,真空度60Pa。