text <-  "the slurry includes: attrition pellet, oxidant, amino acid and water."

corpus_text <- VCorpus(VectorSource(text))
content(corpus_text[[1]])

BigramTokenizer <- function(x) NGramTokenizer(x, Weka_control(min = 1, max = 3))
dtm <-  DocumentTermMatrix(corpus_text, control = list(tokenize = BigramTokenizer))
mat <- as.matrix(dtm)
colnames(mat)

 [1] "acid"                      "acid and"                  "acid and water"
 [4] "amino"                     "amino acid"                "amino acid and"
 [7] "and"                       "and water"                 "attrition"
[10] "attrition pellet"          "attrition pellet oxidant"  "includes"
[13] "includes attrition"        "includes attrition pellet" "oxidant"
[16] "oxidant amino"             "oxidant amino acid"        "pellet"
[19] "pellet oxidant"            "pellet oxidant amino"      "slurry"
[22] "slurry includes"           "slurry includes attrition" "the"
[25] "the slurry"                "the slurry includes"       "water"