Implementation and evaluation of the pulse field gradient technique for the prediction of soluble solids content of fruit juices and soluble solids content and defects in apple tissue using a low frequency proton magnetic resonance sensor
Abstract
The pulsed field gradient technique (PFG) was implemented in a 5.40 MHz $\sp1$H-MR system. A quadrupole coil was used for applying 10 to 15 G/cm gradient pulses. The self-diffusion coefficient of water, $\rm D\sb{w},$ and spin-spin relaxation time, T$\sb2,$ were measured in aqueous solutions of citric acid and/or Na-citrate buffer. Soluble solids of the solutions ranged from 0% to 16%. Juices tested and refractometer brix ranges were 0 to 11% brix in apple juice, 9 to 17% brix in red grape juice, and 21 to 34% brix in orange juice. Tissue tested was taken from Red Delicious, Golden Delicious, and Granny Smith apples. The three varieties of apples had refractometer brixes ranging from 10 to 15%. For this system, the coefficients of variation for T$\sb2$ and $\rm D\sb{w}$ measurements were 10% and 5%, respectively. Buffering and pH affected $\rm D\sb{w}$ by affecting soluble solids levels. The r$\sp2$ for linear regression of $\rm D\sb{w}$ versus refractometer brix was greater than 0.88 for all juices and aqueous solutions tested. $\rm D\sb{w}$ and T$\sb2$ were measured for bruised and unbruised tissue taken from the three apple varieties. $\rm D\sb{w}$ varied with level of both soluble and insoluble solids. Water core and internal browning did not influence $\rm D\sb{w}$ of tissue samples. However, they caused statistically significant differences ($\alpha$ = 0.05) in T$\sb2$ values. T$\sb2$ values for bruised apple tissue were 0.12 to 0.135 sec lower than T$\sb2$ values for good apple tissue. Titratable acids decreased an average of 43% in bruised compared to unbruised apple tissue. T$\sb2$ values for watercore tissue were 0.08 to 0.0935 sec lower than values for good tissue. Apple tissue with internal browning had T$\sb2$ values 0.25 seconds lower than values of good apple tissue. T$\sb2$ varied from 0.8 to 1.2 seconds in good apple tissue. The brix in a watercore apple varied with position. In the watercore tissue, the refractometer brix had an intermediate value (12.5 to 13.5%), compared to a higher brix from tissue around the water core (13 to 16%), and a lower brix from tissue farther away (10.5 to 11.5%).
Degree
Ph.D.
Advisors
Stroshine, Purdue University.
Subject Area
Agricultural engineering|Food science
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