Profiling Taste and Aroma Compound Metabolism during Apricot Fruit Development and Ripening

Effect of SO2 on sugars, indicators of Maillard reaction, and browning in dried apricots during storage

BACKGROUND

The effect of sulfur dioxide (SO₂ ) concentration was determined on sugars and indicators in the Maillard reaction (MR), and on browning, in sulfured, dried apricots (SDAs) during storage at 4, 20 and 30 °C for 379 days.

RESULTS

As SO₂ concentration increased, the content of reducing sugars involved in the MR also increased. The preventive effect of SO₂ on the MR could not result from the binding of SO₂ to reducing sugars. Before storage, furosine was detected in the non-SDAs but 5-hydroxymethylfurfural (HMF) was not detected. Even the lowest SO₂ concentration (451 mg kg^-1 ) was sufficient to prevent the formation of furosine and HMF during drying of apricots.

CONCLUSION

Formation of furosine and HMF in all samples during storage at 20 and 30 °C for 379 days indicated that SO₂ could not prevent the first and intermediate stages of MR in SDAs during storage. Thus, the main prevention effect of SO₂ on browning in SDAs occurred during drying, not storage. © 2018 Society of Chemical Industry.

Effect of fruit maturity level on quality, sensory properties and volatile composition of two common apricot (Prunus armeniaca L.) varieties

The effect of maturity level on fruit quality properties, volatile composition and sensory attributes was investigated in two important apricot varieties (Hacıhaliloğlu and Kabaaşı). The soluble solid content was used as the maturity index for the classification of apricots according to their maturity levels as immature (14-20 °Brix), mature (20-24 °Brix) and over-mature (> 24°Brix). Changes in the volatile composition of samples at different maturity levels were characterized using headspace solid phase micro-extraction gas chromatography-mass spectrometry. The results showed that the quality attributes of the Kabaaşı were affected to a lesser extent by the maturity level than Hacıhaliloğlu. From the immature to over-mature, fruit weight, dry matter and pH increased while firmness and titratable acidity decreased (p < 0.05) in both varieties. Volatile composition was affected by both apricot variety and maturation levels. The main volatiles were aldehydes, alcohols, ketones, esters, terpenes and hydrocarbons. Compared to Kabaaşı, the concentrations of the volatile compounds were higher in Hacıhaliloğlu regardless of the maturity levels. Among the samples, Hacıhaliloğlu at over-mature level received the highest "overall liking" score. The principal component analysis made on the measured quality attributes allowed the discrimination of apricot varieties and their maturity levels.

Shikimate Induced Transcriptional Activation of Protocatechuate Biosynthesis Genes by QuiR, a LysR-Type Transcriptional Regulator, in Listeria monocytogenes

Listeria monocytogenes is a common foodborne bacterial pathogen that contaminates plant and animal consumable products. The persistent nature of L. monocytogenes is associated with millions of dollars in food recalls annually. Here, we describe the role of shikimate in directly modulating the expression of genes encoding enzymes for the conversion of quinate and shikimate metabolites to protocatechuate. In L. monocytogenes, these genes are found within two operons, named qui1 and qui2. In addition, a gene named quiR, encoding a LysR-Type Transcriptional Regulator (QuiR), is located immediately upstream of the qui1 operon. Transcriptional lacZ-promoter fusion experiments show that QuiR induces gene expression of both qui1 and qui2 operons in the presence of shikimate. Furthermore, co-crystallization of the QuiR effector binding domain in complex with shikimate provides insights into the mechanism of activation of this regulator. Together these data show that upon shikimate accumulation, QuiR activates the transcription of genes encoding enzymes involved in shikimate and quinate utilization for the production of protocatechuate. Furthermore, the accumulation of protocatechuate leads to the inhibition of Listeria growth. Since protocatechuate is not known to be utilized by Listeria, its role is distinct from those established in other bacteria.