In-Situ Measurement of Fresh Produce Respiration Using a Modular Sensor-Based System

• Main Authors: Nandita Keshri, Ingo Truppel, Werner B. Herppich, Martin Geyer, Cornelia Weltzien, Pramod V. Mahajan
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: Sensors
• Subjects: Dynamic Controlled Atmosphere (DCA) storage; Respiratory Quotient (RQ); DCA-RQ; apples; strawberries; O₂ and CO₂ sensors
• Online Access: https://www.mdpi.com/1424-8220/20/12/3589

In situ, continuous and real-time monitoring of respiration (R) and respiratory quotient (RQ) are crucial for identifying the optimal conditions for the long-term storage of fresh produce. This study reports the application of a gas sensor (RMS88) and a modular respirometer for in situ real-time monitoring of gas concentrations and respiration rates of strawberries during storage in a lab-scale controlled atmosphere chamber (190 L) and of Pinova apples in a commercial storage facility (170 t). The RMS88 consisted of wireless O₂ (0% to 25%) and CO₂ sensors (0% to 0.5% and 0% to 5%). The modular respirometer (3.3 L for strawberries and 7.4 L for apples) consisted of a leak-proof arrangement with a water-containing base plate and a glass jar on top. Gas concentrations were continuously recorded by the RMS88 at regular intervals of 1 min for strawberries and 5 min for apples and, in real-time, transferred to a terminal program to calculate respiration rates (<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi mathvariant="normal">R</mi> <mrow> <msub> <mi mathvariant="normal">O</mi> <mn>2</mn> </msub> </mrow> </msub> </mrow> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi mathvariant="normal">R</mi> <mrow> <msub> <mrow> <mi>CO</mi> </mrow> <mn>2</mn> </msub> </mrow> </msub> </mrow> </semantics> </math> </inline-formula>) and RQ. Respiration measurement was done in cycles of flushing and measurement period. A respiration measurement cycle with a measurement period of 2 h up to 3 h was shown to be useful for strawberries under air at 10 °C. The start of anaerobic respiration of strawberries due to low O₂ concentration (1%) could be recorded in real-time. <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi mathvariant="normal">R</mi> <mrow> <msub> <mi mathvariant="normal">O</mi> <mn>2</mn> </msub> </mrow> </msub> </mrow> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi mathvariant="normal">R</mi> <mrow> <msub> <mrow> <mi>CO</mi> </mrow> <mn>2</mn> </msub> </mrow> </msub> </mrow> </semantics> </math> </inline-formula> of Pinova apples were recorded every 5 min during storage and mean values of 1.6 and 2.7 mL kg⁻¹ h⁻¹, respectively, were obtained when controlled atmosphere (CA) conditions (2% O₂, 1.3% CO₂ and 2 °C) were established. The modular respirometer was found to be useful for in situ real-time monitoring of respiration rate during storage of fresh produce and offers great potential to be incorporated into RQ-based dynamic CA storage system.