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

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 ( RO2 and RCO2 ) 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. RO2 and RCO2 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

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

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 ( RO2 and RCO2 ) 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. RO2 and RCO2 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

Discrete ex situ and continuous in situ real-time respiration rate measurements of fresh produce using a novel automated dynamic approach

Fresh produce respiration rate is a useful indicator of metabolic state often used in postharvest research to determine physiological differences between factors. Static (no flow) and dynamic (constant flow) measurements are two types of methods that exist for determining respiration rate in fresh produce. Implementation of an automated real-time respiration method, using a dynamic measurement, for measuring respiration rates of fresh produce in discrete (ex situ) and continuous (in situ) set-ups has been established. Discrete methods were performed on fresh (green) black pepper within 3 L hermetically sealed containers with constant flow rates of 400 mL min-1 and 1 L min-1, respectively. Continuous respiration measurements were also obtained in situ for fresh black pepper stored under air (1.8 L min-1) at 5°C, and avocado fruit stored under air and controlled atmosphere environment (ca. 10 kPa CO2 and 10 kPa O2; 400 mL min-1), at 20°C. In addition, simultaneous automated recordings of O2 and CO2 enabled accurate respiratory quotient (RQ) values to be determined for avocado throughout storage. Application of the continuous dynamic in situ measurements can also provide a more realistic assessment of physiological change / behaviour under real-world storage conditions. In this paper, we discuss the application of both discrete and continuous dynamic methods as powerful research techniques for measuring respiration rate in postharvest research

Pathogenic Fusarium oxysporum f. sp. cepae growing inside onion bulbs emits volatile organic compounds that correlate with the extent of infection

Diseases develop during the storage of onions. To minimize losses, new methods are needed to identify diseased bulbs early in storage. Volatile organic compounds (VOCs), the respiration rate, weight loss, and the dry matter content were investigated for 1-7 weeks post inoculation of bulbs with water (control) and two strains (Fox006 or Fox260) of Fusarium oxysporum f. sp. cepae. Photos, multispectral image analysis, and real-time polymerase chain reaction (PCR) showed no infection in the control onions, weak pathogenic infection in Fox006-onions, and strong pathogenic infection in Fox260-onions at week 7 post inoculation. Infected bulbs exhibited increased respiration rate, increased VOC emission rate, and increased weight loss. The control and Fox006-onions did not respond to inoculation and had similar reaction pattern. Forty-three different VOCs were measured, of which 17 compounds had sulfur in their chemical structure. 1-Propanethiol, methyl propyl sulfide, and styrene were emitted in high concentrations and were positively correlated with the extent of infection (r = 0.82 - 0.89). Therefore, these compounds were the most promising volatile markers of Fusarium basal rot infection. For the first time, we show that the extent of fungal infection determined by real-time PCR in onion bulbs is related with VOC emission.Peer reviewe

Intraspecific variation in the metabolism of juvenile Atlantic salmon salmo salar and northern pike esox lucius

Basal metabolic rate (BMR), the sum of maintenance energy costs, represents a major component of the energy budgets of ectothermic vertebrates and varies between individuals within a species. Individual ectotherms are generally assumed to have a constant BMR at any given temperature. A strategy of flexibility in BMR might have evolved to cope with differing environmental conditions. Within-individual variation in BMR was examined in two fishes, juvenile Atlantic salmon Salmo salar and juvenile northern pike Esox lucius, whilst the effects of exercise and ration on BMR, maximum metabolic rate (MMR), enzyme levels and body composition were studied in detail for pike. In the first part of the study, measurements of BMR were made for first-summer Atlantic salmon parr at rest by respirometry. In 1996, initial measurements of BMR were made for 25 fish held in a stock tank. Fish were then allocated in small groups to channels to represent a change in environment and BMR re-measured after a period of several weeks. The procedure was repeated for 30 fish in the summer of 1997, when fish were given a reduced food ration. Variation in BMR in each experiment was analysed for individual fish, and for all fish using a linear mixed model. There were statistically significant differences in BMR values between the two times, the within-individual, between-time variation representing approximately ± 21% of BMR in 1996 and ± 28% of BMR in 1997. Reduced-rafion fish (1997) displayed a significant decrease in the mean elevation of the allometric scaling relationship between body mass and BMR between time periods. To further explore possible mechanisms for flexibility in BMR and relationships with MMR, juvenile pike were used. Initial measurements of BMR and MMR (following exhaustive exercise) were made and factorial metabolic scope calculated (MMR/BMR). Fish were then split into a high ration no-exercise group (n = 10), low ration no-exercise group (n = 10) and sustained exercise group (n = 13). Initial measurements were termed time 1, with subsequent measurements made after approximately 3 weeks (time 2) and 11 weeks (time 3). Exercised fish had a significantly larger MMR and scope following 3 weeks of sustained swimming. For all fish there were significant correlations between BMR and MMR at times 1 and 3 but not at time 2.After the oxygen measurements made at time 3 all fish were humanely killed. Maximal enzyme assays were performed on six tissues for each remaining fish (n = 30). Levels of each of two enzymes (citrate synthase, CS, and lactate dehydrogenase, LDH, measured in the direction of lactate oxidation) were found to be similar between treatment groups for respective tissues. Total CS activity levels and LDH levels were highest in the heart and red muscle. In general there was little difference in the relative organ masses of fish exposed to different treatments. It is concluded that in these two fish species with very different life styles, between- and within- individual variation in BMR (salmon & pike) and MMR (pike only) is apparent and that differences in ration and exercise influence individual physiology

Energy Flow in a Floodplain Aquifer Ecosystem

We developed an energy budget to identify energy sources for the invertebrate community of a large 20 km2 floodplain aquifer, based on biomass distributions, organismal respirometry, in situ community respiration, mesocosm and microcosm experiments, stable isotopes and invertebrate gut contents. The invertebrate respiration scaling exponent was 0.474 (+/- 0.068, 95% CI) across six orders in body mass, which is significantly lower than the ¾ power scaling predicted by metabolic theory. Invertebrate production was dominated by copepods (Diacyclops, Acanthocyclops, Bryocamptus), Stygobromus amphipods, and amphibiont stoneflies, and ranged from 26.9 to 4200 mg C/m3 sediment/year. Production and density showed a U-shaped response to dissolved oxygen (high production at both low and high oxygen concentrations). Production declined exponentially with depth for most sites, but at sites with orthograde oxygen profiles there was an exponential increase at the oxycline. Aerobic microbial community production ranged from 1210 to 2020 mg C/m3 sediment/year, also showing a U-shaped response to oxygen. System respiratory quotient (RQ) ranged from ≈ 0 to 9.5, indicating a significant contribution of anaerobic production to system energy flow. We documented multiple lines of evidence for DOC (soil, river) and buried POM carbon sources, however POM was by far the largest carbon reservoir in the aquifer at ≈ 108 (to 1010) mg C/ m3 sediment. Energy from POM breakdown was the only source sufficient to explain microbial and invertebrate production. Carbon stable isotope signatures showed strong levels of depletion for invertebrates (δ13C -25‰ to -70‰). These results suggest a significant anaerobic subsidy of aerobic food webs in the subsurface, and a potential methane subsidy of 10% to 99% of invertebrate energy flow. Oxygen showed high, non-random, spatial and temporal variation across the aquifer, with a large scale decline in oxygen along the axis of the floodplain, and distinct hotspots of low oxygen. Low oxygen hotspots corresponded with migration of stonefly nymphs 100’s of meters into the aquifer. The U-shaped responses and biogeochemical trends suggest a major threshold at bulk oxygen concentrations of 3-5 mg/l. Collectively, these findings indicate the role of dissolved oxygen as a key variable in groundwater ecosystems

Risk Assessment of Recirculation Systems in Salmonid Hatcheries

To be able to judge whether existing legislation is adequate in safeguarding fish welfare in hatcheries where water is recirculated, the Norwegian Food Safety Authority requested the Norwegian Scientific Committee for Food Safety (VKM) to conduct an assessment of the current situation and whether, or to which degree, a risk of injury, disease or other unnecessary suffering exists. The assessment is limited to salmon and rainbow trout in freshwater systems. Based on literature data and practical experiences from recirculating aquaculture systems (RAS), possible environmental effects on fish welfare were assessed. It is clear that there is a risk that the water quality in RAS can deteriorate and cause severely compromised welfare for the fish. On the other hand, a well-managed RAS can in fact stabilize, or even improve water quality, resulting in better welfare compared with some flow-through systems

The measurement of draught ruminant energy expenditure in the field

The aim of this work was to improve and validate the Oxylog portable oxygen consumption meter for use with draught ruminants, and to test its ability to estimate the energy expenditure of these animals in the field.Few data were available on the energy costs of the various tasks that draught ruminants perform and it was expected that the calorific factors established during laboratory experiments may not necessarily reflect the energy consumption during field work with farmers. This could have important implications in the establishment of the nutritional requirements of draught ruminants.A review of the literature on the various techniques and instruments available for the field measurement of energy consumption was carried out.A new facemask for use with the Oxylog was designed and the Oxylog equipment with this mask was validated against the open circuit gas analysis system available at the Centre for Tropical Veterinary Medicine in Edinburgh. It was found that the Oxylog, on average, overestimated oxygen consumption, as measured by the gas analysis system, by 1.5 %.In the second experiment, carried out with buffaloes and oxen pulling carts on the Unipalma oil-palm plantation in Meta, Colombia, the modified Oxylog system was tested in the field. Technically, the method worked satisfactorily, although the small digital displays on the Oxylog were difficult to read, and the measurements obtained generally agreed with the more established calculation methods of estimating energy consumption. It was concluded that the use of the modified Oxylog was an accurate and reliable method for the estimation of energy expenditure in the field. Insufficient time, however, was available to train the animals to wear the facemask and to accustom them to the experimental procedures, hence, the acceptance of the mask was low. The use of a constant value for the energy cost of walking over various terrains and the difficulty in accurately defining the animals' respiratory quotient, were also thought to have affected the results.In the third experiment, the influence of soil consistency on the energy cost of walking and the efficiency of working in Bunaji (Bos indicus) draught bulls in the sub-humid zone of Nigeria was investigated. These experiments were carried out in collaboration with the International Livestock Centre for Africa. A dataviewer was designed to facilitate data collection. To ensure that the respiratory quotient only varied between 0.8 and 1.0 the animals were fed 3 kg of concentrates, 1 h before the start of the experiments so that they were primarily metabolising carbohydrates. Eight experimental animals were trained over a period of four weeks and the mask acceptance rate was 100 %. The energy cost of walking on the different soils varied from 1.47 J/m/kg to 3.30 J/m/kg. Ploughing doubled or more than doubled the energy cost of walking on the soils investigated. Although the consistency of the soil did not influence the efficiency of doing work, both the speed of walking and work¬ ing, and the distance average draught force were affected. A simple method to estimate the energy cost of walking based on the speed of walking on soils of different consistencies was proposed. It was further established that it would be more efficient to cultivate soils before they became inundated with water, because as they became wetter more time, effort and energy were needed for cultivation per unit area.It was concluded that the modified Oxylog, although its use will be largely restricted to trained animals being investigated by research organisations, is a useful and reliable tool in draught ruminant field calorimetry