Research progress on detection methods of N-dimethylnitrosamine in foods

N-dimethylnitrosamine is one of the most toxic nitrosamine compounds and can be produced in the process of food processing or storage. The detection methods are various with tedious operation and low accuracy. QuEChERS pretreatment combined with GC/LC-MS has been widely used in the determination of N-dimethylnitrosamine in food due to its advantages of simple operation， good extraction and purification， high sensitivity， stable recovery and effective improvement of detection rate and throughput. The pretreatment methods， detection equipment and detection parameters of N-dimethylnitrosamine in food were compared to analyze the advantages and disadvantages of different methods

Estimation of leaf area index and plant area index of a submerged macrophyte canopy using digital photography.

Non-destructive estimation using digital cameras is a common approach for estimating leaf area index (LAI) of terrestrial vegetation. However, no attempt has been made so far to develop non-destructive approaches to LAI estimation for aquatic vegetation. Using the submerged plant species Potamogeton malainus, the objective of this study was to determine whether the gap fraction derived from vertical photographs could be used to estimate LAI of aquatic vegetation. Our results suggested that upward-oriented photographs taken from beneath the water surface were more suitable for distinguishing vegetation from other objects than were downward-oriented photographs taken from above the water surface. Exposure settings had a substantial influence on the identification of vegetation in upward-oriented photographs. Automatic exposure performed nearly as well as the optimal trial exposure, making it a good choice for operational convenience. Similar to terrestrial vegetation, our results suggested that photographs taken for the purpose of distinguishing gap fraction in aquatic vegetation should be taken under diffuse light conditions. Significant logarithmic relationships were observed between the vertical gap fraction derived from upward-oriented photographs and plant area index (PAI) and LAI derived from destructive harvesting. The model we developed to depict the relationship between PAI and gap fraction was similar to the modified theoretical Poisson model, with coefficients of 1.82 and 1.90 for our model and the theoretical model, respectively. This suggests that vertical upward-oriented photographs taken from below the water surface are a feasible alternative to destructive harvesting for estimating PAI and LAI for the submerged aquatic plant Potamogeton malainus

Summary statistics for plant area index (PAI), leaf area index (LAI) and gap fraction in our study plots (i.e. incubators).

*<p>Standard deviation.</p

Variation in the F’ statistic for digital number (DN) differences between background (sky) and vegetation pixels with time of day ranging from before sunrise (05:00 h) to after sunset (19:00 h).

<p>Variation in the F’ statistic for digital number (DN) differences between background (sky) and vegetation pixels with time of day ranging from before sunrise (05:00 h) to after sunset (19:00 h).</p

The influence of photograph orientation on digital number (DN) differences between vegetation and background pixels in vertical photographs of aquatic vegetation.

<p>A and B show vertical upward- and downward-oriented photographs, respectively. Histograms of DNs for red, blue and green bands are also shown for upward-oriented (A-Red, A-Blue and A-Green) and downward-oriented (B-Red, B-Blue and B-Green) photographs.</p

Variation in the F’ statistic for DN differences between background (sky) and vegetation pixels in upward-oriented photographs with exposures ranging from 1/1500 s to 1/100 s.

<p>Variation in the F’ statistic for DN differences between background (sky) and vegetation pixels in upward-oriented photographs with exposures ranging from 1/1500 s to 1/100 s.</p

Variation in the F’ statistic for digital number (DN) differences between background (sky) and vegetation pixels in upward-oriented photographs with water turbidity ranging from 2.0 to 30.0 NTU.

<p>Variation in the F’ statistic for digital number (DN) differences between background (sky) and vegetation pixels in upward-oriented photographs with water turbidity ranging from 2.0 to 30.0 NTU.</p

The influence of time of day on differences in digital number (DN) between vegetation and background pixels in vertical upward-oriented photographs.

<p>From A to H, the photographic times were 05:00, 07:00, 09:00, 11:00, 13:00, 15:00, 17:00, and 19:00 h, respectively. A and H were taken before sunrise and after sundown, respectively, when there was no direct sunlight.</p

The influence of water turbidity on digital number (DN) differences between vegetation and background pixels in vertical upward-oriented photographs.

<p>From A to F, turbidity values were 2.0, 6.0, 10.0, 20.0, 25.0 and 30.0 NTU, respectively.</p

The relationship between vertical gap fraction calculated from upward-oriented photographs and plant area index (PAI, A), and leaf area index (LAI, B) calculated using a destructive harvesting approach.

<p>The relationship between vertical gap fraction calculated from upward-oriented photographs and plant area index (PAI, A), and leaf area index (LAI, B) calculated using a destructive harvesting approach.</p