- The objectives of this study are to 1) qualitatively and quantitatively measure the odor-active compounds in ‘Marion’ blackberry; 2) compare the aroma profiles of advanced selections and new cultivars of thornless blackberry cultivars with ‘Marion’; 3) study the development of furaneol in ‘Marion’ during ripening and; 4) investigate the distribution of odor-active compounds and their precursors in the selections that contributed to ‘Marion’s pedigree.
Aroma of ‘Marion’ blackberry was analyzed with LiChrolut-EN solid-phase extraction (SPE) and microvial insert thermal desorption GC-MS-olfactometry. The results showed that LiChrolut-EN had limited absorption of sugars, pigments, and other non-volatile compounds, while extracting a vast majority of polar and non-polar aroma compounds. The potential odorants identified in ‘Marion’ included furaneol, linalool, β-ionone, hexanal, ethyl hexanoate, hexyl acetate, 2-heptanol, cis-3-hexenol, and trans-2-hexenol. Furaneol was considered the impact characteristic aroma compound in ‘Marion’. A method used for the determination of furaneol was further developed using SPE-GC-MS operated in the selected ion mode. Furaneol could be effectively isolated by LiChrolut-EN cartridge and completely eluted out with 1 mL of methanol, which could be directly analyzed on GC-MS using an automated microvial insert thermal desorption technique without further purification and concentration. The method proved sensitive with good recovery and reproducibility. A modified method using SPE-GC-MS with poly(vinylpolypyrrolidone) to remove pigments in the berry samples was further
developed to quantify other odor-active compounds. The method was reproducible, had satisfactory recoveries for over 50 selected compounds, and had minimum decomposition of glycosides and pigments.
The aroma constituents of ‘Black Diamond’ blackberry were identified and the predominant odor-active compounds in ‘Black Diamond’ were ethyl butanoate, ethyl hexanoate, 1-octen-3-one, 2-heptanol, cis-3-hexenol, nonanal, trans-2-hexenol, methional, linalool, ethyl 3-hydroxyhexanoate, α-ionone, β-ionone, and furaneol. A comparison of volatiles in ‘Black Diamond’ and ‘Marion’ was conducted using SPE-GC-MS and stir bar sorptive extraction (SBSE)-GC-MS over two growing seasons. Although seasonal variations were present, the overall volatile profile in ‘Black Diamond’ and ‘Marion’ were very similar, but the concentrations of some aroma compounds varied greatly. Odor activity values (OAVs) indicated that furaneol, linalool, β-ionone, and hexanal were the most important odor-active compounds in ‘Marion’, while in ‘Black Diamond’, the most important compounds were linalool, β-ionone, furaneol, and 2-heptanol. The major difference between two cultivars was that ‘Marion’ had a five times higher OAV of furaneol than ‘Black Diamond’, while ‘Black Diamond’ had a three times higher OAV of linalool than ‘Marion’. A flavor comparison of other thornless blackberry cultivars including ‘Thornless Evergreen’, ‘Black Pearl’, ‘Nightfall’, ORUS 1843-3, ‘Waldo’, NZ 9351-4, and ‘Chester Thornless’ with ‘Marion’ was further conducted. The results indicated that the blackberries had very diverse flavor profiles. Furaneol, linalool, β-ionone, 2-heptanol, and carvone were the major aroma compounds in blackberries. High OAVs of furaneol, linalool, and β-ionone in ‘Marion’, ‘Black Diamond’, ‘Black Pearl’, ORUS 1843-3, and NZ 9351-4 accounted for their similar fresh fruity, strawberry and raspberry aroma, while high OAVs of 1-octen-3-ol, myrtenol, eugenol, and α-terpineol in ‘Waldo’, ‘Nightfall’, ‘Chester Thornless’, and ‘Thornless Evergreen’ accounted for their vegetal, woody, and moldy aroma. Instrumental analysis matched with descriptive sensory analysis.
Free furaneol and furaneol glycoside were further studied in ‘Marion’ during ripening. Free furaneol was analyzed by SPE-GC-MS with PVPP decoloration of juice. Furaneol glucosides were isolated with XAD-2 sorbent, hydrolyzed with β-
glucosidase, and the released aglycone was analyzed using SPE-GC-MS. Seasonal variation was observed; however, the tendency of the change in each year’s berry flavor profile was similar. Dramatic chemical composition changes occurred after the mottled stage. Only trace levels of free furaneol and furaneol glycoside were detected before the mottled stage. Between the mottled and shiny-black stages, free furaneol dramatically increased from 1.4 mg/kg to 9.0 mg/kg, and continuously increased into the overripe stage to 22 mg/kg; while furaneol glucoside increased from 0.8 mg/kg to 4.0 mg/kg, and dramatically increased into the overripe stage to 34 mg/kg – a much higher concentration than the free furaneol at the same stage.
The distribution of volatile constituents and volatile precursors in the genotypes that are in ‘Marion’s pedigree was investigated. Volatiles were analyzed using SBSE-GC-MS and SPE-GC-MS. Volatile precursors were isolated with C18 cartridge, enzymatically hydrolyzed, and released aglycons were analyzed using GC-MS. The results indicated each cultivar in the ‘Marion’ pedigree had a specific volatile and volatile precursor pattern. Wild ‘Himalaya’ had predominant volatiles of terpenes and furanones. ‘Santiam’ also had dominant volatile of terpenes. Their progeny, ‘Chehalem’, had a combination of these characteristics. ‘Meeker’ raspberry was dominated by norisoprenoids, lactones, and acids. Its progenies, ‘Logan’ and ‘Olallie’, were similar in norisoprenoid dominance. ‘Marion’, from the cross of ‘Chehalem’ and ‘Olallie’, contained almost all the volatile compounds, but the concentrations of most compounds were more evenly distributed than other cultivars. Some key compounds such as linalool, β-ionone, and furaneol had a unique distribution. ‘Marion’ had a moderate level of linalool. ‘Olallie’ and ‘Logan’ had a significantly high linalool level, while the other stream had much lower linalool content. The concentrations of β-ionone in ‘Marion’, ‘Chehalem’, ‘Santiam’, and ‘Himalaya’ were low, while the cultivars in the other stream had higher β-ionone levels. The β-ionone content in ‘Meeker’ was over 40 times the amount in other cultivars. The concentration of furaneol in ‘Marion’ was higher than in its parents, ‘Chehalem’ and ‘Olallie’. The distribution of volatile precursor pattern in the ‘Marion’ pedigree was similar to the free form. The chiral isomeric ratios of 13 pairs of compounds were studied using a Cyclosil B column. Strong chiral isomeric preference was observed for the most of compounds, and each cultivar had its unique chiral isomeric ratio distribution.